Add nullable annotations to Microsoft.AspNetCore.Mvc.Abstractions (#22993)

* Add nullable annotations to Microsoft.AspNetCore.Mvc.Abstractions
Contributes to https://github.com/dotnet/aspnetcore/issues/5680

* Changes per PR comments

* Changes per PR comments

* Fixup

src/Mvc/Mvc.Abstractions/ref/Microsoft.AspNetCore.Mvc.Abstractions.csproj

@@ -2,6 +2,7 @@
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
     <TargetFrameworks>$(DefaultNetCoreTargetFramework)</TargetFrameworks>
+    <Nullable>annotations</Nullable>
   </PropertyGroup>
   <ItemGroup Condition="'$(TargetFramework)' == '$(DefaultNetCoreTargetFramework)'">
     <Compile Include="Microsoft.AspNetCore.Mvc.Abstractions.netcoreapp.cs" />

src/Mvc/Mvc.Abstractions/ref/Microsoft.AspNetCore.Mvc.Abstractions.netcoreapp.cs

@@ -33,10 +33,10 @@ namespace Microsoft.AspNetCore.Mvc.Abstractions
     public partial class ActionDescriptor
     {
         public ActionDescriptor() { }
-        public System.Collections.Generic.IList<Microsoft.AspNetCore.Mvc.ActionConstraints.IActionConstraintMetadata> ActionConstraints { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public System.Collections.Generic.IList<Microsoft.AspNetCore.Mvc.ActionConstraints.IActionConstraintMetadata>? ActionConstraints { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
-        public Microsoft.AspNetCore.Mvc.Routing.AttributeRouteInfo AttributeRouteInfo { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public Microsoft.AspNetCore.Mvc.Routing.AttributeRouteInfo? AttributeRouteInfo { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
         public System.Collections.Generic.IList<Microsoft.AspNetCore.Mvc.Abstractions.ParameterDescriptor> BoundProperties { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
-        public virtual string DisplayName { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public virtual string? DisplayName { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
         public System.Collections.Generic.IList<object> EndpointMetadata { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
         public System.Collections.Generic.IList<Microsoft.AspNetCore.Mvc.Filters.FilterDescriptor> FilterDescriptors { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
         public string Id { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
@@ -58,7 +58,7 @@ namespace Microsoft.AspNetCore.Mvc.Abstractions
     {
         public ActionInvokerProviderContext(Microsoft.AspNetCore.Mvc.ActionContext actionContext) { }
         public Microsoft.AspNetCore.Mvc.ActionContext ActionContext { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
-        public Microsoft.AspNetCore.Mvc.Abstractions.IActionInvoker Result { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public Microsoft.AspNetCore.Mvc.Abstractions.IActionInvoker? Result { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
     }
     public partial interface IActionDescriptorProvider
     {
@@ -143,8 +143,8 @@ namespace Microsoft.AspNetCore.Mvc.ApiExplorer
     {
         public ApiDescription() { }
         public Microsoft.AspNetCore.Mvc.Abstractions.ActionDescriptor ActionDescriptor { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
-        public string GroupName { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public string? GroupName { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
-        public string HttpMethod { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public string? HttpMethod { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
         public System.Collections.Generic.IList<Microsoft.AspNetCore.Mvc.ApiExplorer.ApiParameterDescription> ParameterDescriptions { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
         public System.Collections.Generic.IDictionary<object, object> Properties { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
         public string RelativePath { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
@@ -160,21 +160,21 @@ namespace Microsoft.AspNetCore.Mvc.ApiExplorer
     public partial class ApiParameterDescription
     {
         public ApiParameterDescription() { }
-        public Microsoft.AspNetCore.Mvc.ModelBinding.BindingInfo BindingInfo { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public Microsoft.AspNetCore.Mvc.ModelBinding.BindingInfo? BindingInfo { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
-        public object DefaultValue { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public object? DefaultValue { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
         public bool IsRequired { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
         public Microsoft.AspNetCore.Mvc.ModelBinding.ModelMetadata ModelMetadata { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
         public string Name { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
         public Microsoft.AspNetCore.Mvc.Abstractions.ParameterDescriptor ParameterDescriptor { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
-        public Microsoft.AspNetCore.Mvc.ApiExplorer.ApiParameterRouteInfo RouteInfo { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public Microsoft.AspNetCore.Mvc.ApiExplorer.ApiParameterRouteInfo? RouteInfo { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
         public Microsoft.AspNetCore.Mvc.ModelBinding.BindingSource Source { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
         public System.Type Type { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
     }
     public partial class ApiParameterRouteInfo
     {
         public ApiParameterRouteInfo() { }
-        public System.Collections.Generic.IEnumerable<Microsoft.AspNetCore.Routing.IRouteConstraint> Constraints { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public System.Collections.Generic.IEnumerable<Microsoft.AspNetCore.Routing.IRouteConstraint>? Constraints { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
-        public object DefaultValue { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public object? DefaultValue { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
         public bool IsOptional { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
     }
     public partial class ApiRequestFormat
@@ -194,9 +194,9 @@ namespace Microsoft.AspNetCore.Mvc.ApiExplorer
         public ApiResponseType() { }
         public System.Collections.Generic.IList<Microsoft.AspNetCore.Mvc.ApiExplorer.ApiResponseFormat> ApiResponseFormats { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
         public bool IsDefaultResponse { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
-        public Microsoft.AspNetCore.Mvc.ModelBinding.ModelMetadata ModelMetadata { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public Microsoft.AspNetCore.Mvc.ModelBinding.ModelMetadata? ModelMetadata { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
         public int StatusCode { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
-        public System.Type Type { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public System.Type? Type { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
     }
     public partial interface IApiDescriptionProvider
     {
@@ -218,8 +218,8 @@ namespace Microsoft.AspNetCore.Mvc.Filters
         public ActionExecutedContext(Microsoft.AspNetCore.Mvc.ActionContext actionContext, System.Collections.Generic.IList<Microsoft.AspNetCore.Mvc.Filters.IFilterMetadata> filters, object controller) : base (default(Microsoft.AspNetCore.Mvc.ActionContext), default(System.Collections.Generic.IList<Microsoft.AspNetCore.Mvc.Filters.IFilterMetadata>)) { }
         public virtual bool Canceled { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
         public virtual object Controller { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
-        public virtual System.Exception Exception { get { throw null; } set { } }
+        public virtual System.Exception? Exception { get { throw null; } set { } }
-        public virtual System.Runtime.ExceptionServices.ExceptionDispatchInfo ExceptionDispatchInfo { get { throw null; } set { } }
+        public virtual System.Runtime.ExceptionServices.ExceptionDispatchInfo? ExceptionDispatchInfo { get { throw null; } set { } }
         public virtual bool ExceptionHandled { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
         public virtual Microsoft.AspNetCore.Mvc.IActionResult Result { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
     }
@@ -228,26 +228,27 @@ namespace Microsoft.AspNetCore.Mvc.Filters
         public ActionExecutingContext(Microsoft.AspNetCore.Mvc.ActionContext actionContext, System.Collections.Generic.IList<Microsoft.AspNetCore.Mvc.Filters.IFilterMetadata> filters, System.Collections.Generic.IDictionary<string, object> actionArguments, object controller) : base (default(Microsoft.AspNetCore.Mvc.ActionContext), default(System.Collections.Generic.IList<Microsoft.AspNetCore.Mvc.Filters.IFilterMetadata>)) { }
         public virtual System.Collections.Generic.IDictionary<string, object> ActionArguments { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
         public virtual object Controller { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
-        public virtual Microsoft.AspNetCore.Mvc.IActionResult Result { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public virtual Microsoft.AspNetCore.Mvc.IActionResult? Result { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
     }
     public delegate System.Threading.Tasks.Task<Microsoft.AspNetCore.Mvc.Filters.ActionExecutedContext> ActionExecutionDelegate();
     public partial class AuthorizationFilterContext : Microsoft.AspNetCore.Mvc.Filters.FilterContext
     {
         public AuthorizationFilterContext(Microsoft.AspNetCore.Mvc.ActionContext actionContext, System.Collections.Generic.IList<Microsoft.AspNetCore.Mvc.Filters.IFilterMetadata> filters) : base (default(Microsoft.AspNetCore.Mvc.ActionContext), default(System.Collections.Generic.IList<Microsoft.AspNetCore.Mvc.Filters.IFilterMetadata>)) { }
-        public virtual Microsoft.AspNetCore.Mvc.IActionResult Result { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public virtual Microsoft.AspNetCore.Mvc.IActionResult? Result { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
     }
     public partial class ExceptionContext : Microsoft.AspNetCore.Mvc.Filters.FilterContext
     {
         public ExceptionContext(Microsoft.AspNetCore.Mvc.ActionContext actionContext, System.Collections.Generic.IList<Microsoft.AspNetCore.Mvc.Filters.IFilterMetadata> filters) : base (default(Microsoft.AspNetCore.Mvc.ActionContext), default(System.Collections.Generic.IList<Microsoft.AspNetCore.Mvc.Filters.IFilterMetadata>)) { }
         public virtual System.Exception Exception { get { throw null; } set { } }
-        public virtual System.Runtime.ExceptionServices.ExceptionDispatchInfo ExceptionDispatchInfo { get { throw null; } set { } }
+        public virtual System.Runtime.ExceptionServices.ExceptionDispatchInfo? ExceptionDispatchInfo { get { throw null; } set { } }
         public virtual bool ExceptionHandled { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
-        public virtual Microsoft.AspNetCore.Mvc.IActionResult Result { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public virtual Microsoft.AspNetCore.Mvc.IActionResult? Result { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
     }
     public abstract partial class FilterContext : Microsoft.AspNetCore.Mvc.ActionContext
     {
         public FilterContext(Microsoft.AspNetCore.Mvc.ActionContext actionContext, System.Collections.Generic.IList<Microsoft.AspNetCore.Mvc.Filters.IFilterMetadata> filters) { }
         public virtual System.Collections.Generic.IList<Microsoft.AspNetCore.Mvc.Filters.IFilterMetadata> Filters { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
+        [return: System.Diagnostics.CodeAnalysis.MaybeNullAttribute]
         public TMetadata FindEffectivePolicy<TMetadata>() where TMetadata : Microsoft.AspNetCore.Mvc.Filters.IFilterMetadata { throw null; }
         public bool IsEffectivePolicy<TMetadata>(TMetadata policy) where TMetadata : Microsoft.AspNetCore.Mvc.Filters.IFilterMetadata { throw null; }
     }
@@ -349,15 +350,15 @@ namespace Microsoft.AspNetCore.Mvc.Filters
     {
         public ResourceExecutedContext(Microsoft.AspNetCore.Mvc.ActionContext actionContext, System.Collections.Generic.IList<Microsoft.AspNetCore.Mvc.Filters.IFilterMetadata> filters) : base (default(Microsoft.AspNetCore.Mvc.ActionContext), default(System.Collections.Generic.IList<Microsoft.AspNetCore.Mvc.Filters.IFilterMetadata>)) { }
         public virtual bool Canceled { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
-        public virtual System.Exception Exception { get { throw null; } set { } }
+        public virtual System.Exception? Exception { get { throw null; } set { } }
-        public virtual System.Runtime.ExceptionServices.ExceptionDispatchInfo ExceptionDispatchInfo { get { throw null; } set { } }
+        public virtual System.Runtime.ExceptionServices.ExceptionDispatchInfo? ExceptionDispatchInfo { get { throw null; } set { } }
         public virtual bool ExceptionHandled { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
-        public virtual Microsoft.AspNetCore.Mvc.IActionResult Result { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public virtual Microsoft.AspNetCore.Mvc.IActionResult? Result { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
     }
     public partial class ResourceExecutingContext : Microsoft.AspNetCore.Mvc.Filters.FilterContext
     {
         public ResourceExecutingContext(Microsoft.AspNetCore.Mvc.ActionContext actionContext, System.Collections.Generic.IList<Microsoft.AspNetCore.Mvc.Filters.IFilterMetadata> filters, System.Collections.Generic.IList<Microsoft.AspNetCore.Mvc.ModelBinding.IValueProviderFactory> valueProviderFactories) : base (default(Microsoft.AspNetCore.Mvc.ActionContext), default(System.Collections.Generic.IList<Microsoft.AspNetCore.Mvc.Filters.IFilterMetadata>)) { }
-        public virtual Microsoft.AspNetCore.Mvc.IActionResult Result { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public virtual Microsoft.AspNetCore.Mvc.IActionResult? Result { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
         public System.Collections.Generic.IList<Microsoft.AspNetCore.Mvc.ModelBinding.IValueProviderFactory> ValueProviderFactories { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
     }
     public delegate System.Threading.Tasks.Task<Microsoft.AspNetCore.Mvc.Filters.ResourceExecutedContext> ResourceExecutionDelegate();
@@ -366,8 +367,8 @@ namespace Microsoft.AspNetCore.Mvc.Filters
         public ResultExecutedContext(Microsoft.AspNetCore.Mvc.ActionContext actionContext, System.Collections.Generic.IList<Microsoft.AspNetCore.Mvc.Filters.IFilterMetadata> filters, Microsoft.AspNetCore.Mvc.IActionResult result, object controller) : base (default(Microsoft.AspNetCore.Mvc.ActionContext), default(System.Collections.Generic.IList<Microsoft.AspNetCore.Mvc.Filters.IFilterMetadata>)) { }
         public virtual bool Canceled { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
         public virtual object Controller { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
-        public virtual System.Exception Exception { get { throw null; } set { } }
+        public virtual System.Exception? Exception { get { throw null; } set { } }
-        public virtual System.Runtime.ExceptionServices.ExceptionDispatchInfo ExceptionDispatchInfo { get { throw null; } set { } }
+        public virtual System.Runtime.ExceptionServices.ExceptionDispatchInfo? ExceptionDispatchInfo { get { throw null; } set { } }
         public virtual bool ExceptionHandled { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
         public virtual Microsoft.AspNetCore.Mvc.IActionResult Result { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
     }
@@ -382,7 +383,7 @@ namespace Microsoft.AspNetCore.Mvc.Filters
 }
 namespace Microsoft.AspNetCore.Mvc.Formatters
 {
-    public partial class FormatterCollection<TFormatter> : System.Collections.ObjectModel.Collection<TFormatter>
+    public partial class FormatterCollection<TFormatter> : System.Collections.ObjectModel.Collection<TFormatter> where TFormatter : notnull
     {
         public FormatterCollection() { }
         public FormatterCollection(System.Collections.Generic.IList<TFormatter> list) { }
@@ -426,7 +427,7 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
         internal InputFormatterResult() { }
         public bool HasError { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
         public bool IsModelSet { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
-        public object Model { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
+        public object? Model { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
         public static Microsoft.AspNetCore.Mvc.Formatters.InputFormatterResult Failure() { throw null; }
         public static System.Threading.Tasks.Task<Microsoft.AspNetCore.Mvc.Formatters.InputFormatterResult> FailureAsync() { throw null; }
         public static Microsoft.AspNetCore.Mvc.Formatters.InputFormatterResult NoValue() { throw null; }
@@ -445,8 +446,8 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
         public virtual Microsoft.Extensions.Primitives.StringSegment ContentType { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
         public virtual bool ContentTypeIsServerDefined { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
         public virtual Microsoft.AspNetCore.Http.HttpContext HttpContext { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] protected set { } }
-        public virtual object Object { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] protected set { } }
+        public virtual object? Object { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] protected set { } }
-        public virtual System.Type ObjectType { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] protected set { } }
+        public virtual System.Type? ObjectType { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] protected set { } }
     }
     public partial class OutputFormatterWriteContext : Microsoft.AspNetCore.Mvc.Formatters.OutputFormatterCanWriteContext
     {
@@ -460,18 +461,18 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
     {
         public BindingInfo() { }
         public BindingInfo(Microsoft.AspNetCore.Mvc.ModelBinding.BindingInfo other) { }
-        public string BinderModelName { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public string? BinderModelName { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
-        public System.Type BinderType { get { throw null; } set { } }
+        public System.Type? BinderType { get { throw null; } set { } }
-        public Microsoft.AspNetCore.Mvc.ModelBinding.BindingSource BindingSource { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public Microsoft.AspNetCore.Mvc.ModelBinding.BindingSource? BindingSource { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
         public Microsoft.AspNetCore.Mvc.ModelBinding.EmptyBodyBehavior EmptyBodyBehavior { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
-        public Microsoft.AspNetCore.Mvc.ModelBinding.IPropertyFilterProvider PropertyFilterProvider { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public Microsoft.AspNetCore.Mvc.ModelBinding.IPropertyFilterProvider? PropertyFilterProvider { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
-        public System.Func<Microsoft.AspNetCore.Mvc.ActionContext, bool> RequestPredicate { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public System.Func<Microsoft.AspNetCore.Mvc.ActionContext, bool>? RequestPredicate { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
-        public static Microsoft.AspNetCore.Mvc.ModelBinding.BindingInfo GetBindingInfo(System.Collections.Generic.IEnumerable<object> attributes) { throw null; }
+        public static Microsoft.AspNetCore.Mvc.ModelBinding.BindingInfo? GetBindingInfo(System.Collections.Generic.IEnumerable<object> attributes) { throw null; }
-        public static Microsoft.AspNetCore.Mvc.ModelBinding.BindingInfo GetBindingInfo(System.Collections.Generic.IEnumerable<object> attributes, Microsoft.AspNetCore.Mvc.ModelBinding.ModelMetadata modelMetadata) { throw null; }
+        public static Microsoft.AspNetCore.Mvc.ModelBinding.BindingInfo? GetBindingInfo(System.Collections.Generic.IEnumerable<object> attributes, Microsoft.AspNetCore.Mvc.ModelBinding.ModelMetadata modelMetadata) { throw null; }
         public bool TryApplyBindingInfo(Microsoft.AspNetCore.Mvc.ModelBinding.ModelMetadata modelMetadata) { throw null; }
     }
     [System.Diagnostics.DebuggerDisplayAttribute("Source: {DisplayName}")]
-    public partial class BindingSource : System.IEquatable<Microsoft.AspNetCore.Mvc.ModelBinding.BindingSource>
+    public partial class BindingSource : System.IEquatable<Microsoft.AspNetCore.Mvc.ModelBinding.BindingSource?>
     {
         public static readonly Microsoft.AspNetCore.Mvc.ModelBinding.BindingSource Body;
         public static readonly Microsoft.AspNetCore.Mvc.ModelBinding.BindingSource Custom;
@@ -489,11 +490,11 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         public bool IsFromRequest { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
         public bool IsGreedy { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
         public virtual bool CanAcceptDataFrom(Microsoft.AspNetCore.Mvc.ModelBinding.BindingSource bindingSource) { throw null; }
-        public bool Equals(Microsoft.AspNetCore.Mvc.ModelBinding.BindingSource other) { throw null; }
+        public bool Equals(Microsoft.AspNetCore.Mvc.ModelBinding.BindingSource? other) { throw null; }
-        public override bool Equals(object obj) { throw null; }
+        public override bool Equals(object? obj) { throw null; }
         public override int GetHashCode() { throw null; }
-        public static bool operator ==(Microsoft.AspNetCore.Mvc.ModelBinding.BindingSource s1, Microsoft.AspNetCore.Mvc.ModelBinding.BindingSource s2) { throw null; }
+        public static bool operator ==(Microsoft.AspNetCore.Mvc.ModelBinding.BindingSource? s1, Microsoft.AspNetCore.Mvc.ModelBinding.BindingSource? s2) { throw null; }
-        public static bool operator !=(Microsoft.AspNetCore.Mvc.ModelBinding.BindingSource s1, Microsoft.AspNetCore.Mvc.ModelBinding.BindingSource s2) { throw null; }
+        public static bool operator !=(Microsoft.AspNetCore.Mvc.ModelBinding.BindingSource? s1, Microsoft.AspNetCore.Mvc.ModelBinding.BindingSource? s2) { throw null; }
     }
     public partial class CompositeBindingSource : Microsoft.AspNetCore.Mvc.ModelBinding.BindingSource
     {
@@ -524,7 +525,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
     }
     public partial interface IBindingSourceMetadata
     {
-        Microsoft.AspNetCore.Mvc.ModelBinding.BindingSource BindingSource { get; }
+        Microsoft.AspNetCore.Mvc.ModelBinding.BindingSource? BindingSource { get; }
     }
     public partial interface IModelBinder
     {
@@ -607,9 +608,9 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         private readonly object _dummy;
         private readonly int _dummyPrimitive;
         public bool IsModelSet { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
-        public object Model { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
+        public object? Model { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
         public bool Equals(Microsoft.AspNetCore.Mvc.ModelBinding.ModelBindingResult other) { throw null; }
-        public override bool Equals(object obj) { throw null; }
+        public override bool Equals(object? obj) { throw null; }
         public static Microsoft.AspNetCore.Mvc.ModelBinding.ModelBindingResult Failed() { throw null; }
         public override int GetHashCode() { throw null; }
         public static bool operator ==(Microsoft.AspNetCore.Mvc.ModelBinding.ModelBindingResult x, Microsoft.AspNetCore.Mvc.ModelBinding.ModelBindingResult y) { throw null; }
@@ -620,10 +621,10 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
     public partial class ModelError
     {
         public ModelError(System.Exception exception) { }
-        public ModelError(System.Exception exception, string errorMessage) { }
+        public ModelError(System.Exception exception, string? errorMessage) { }
-        public ModelError(string errorMessage) { }
+        public ModelError(string? errorMessage) { }
         public string ErrorMessage { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
-        public System.Exception Exception { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
+        public System.Exception? Exception { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
     }
     public partial class ModelErrorCollection : System.Collections.ObjectModel.Collection<Microsoft.AspNetCore.Mvc.ModelBinding.ModelError>
     {
@@ -632,7 +633,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         public void Add(string errorMessage) { }
     }
     [System.Diagnostics.DebuggerDisplayAttribute("{DebuggerToString(),nq}")]
-    public abstract partial class ModelMetadata : Microsoft.AspNetCore.Mvc.ModelBinding.IModelMetadataProvider, System.IEquatable<Microsoft.AspNetCore.Mvc.ModelBinding.ModelMetadata>
+    public abstract partial class ModelMetadata : Microsoft.AspNetCore.Mvc.ModelBinding.IModelMetadataProvider, System.IEquatable<Microsoft.AspNetCore.Mvc.ModelBinding.ModelMetadata?>
     {
         public static readonly int DefaultOrder;
         protected ModelMetadata(Microsoft.AspNetCore.Mvc.ModelBinding.Metadata.ModelMetadataIdentity identity) { }
@@ -641,15 +642,15 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         public abstract System.Type BinderType { get; }
         public abstract Microsoft.AspNetCore.Mvc.ModelBinding.BindingSource BindingSource { get; }
         public virtual Microsoft.AspNetCore.Mvc.ModelBinding.ModelMetadata ContainerMetadata { get { throw null; } }
-        public System.Type ContainerType { get { throw null; } }
+        public System.Type? ContainerType { get { throw null; } }
         public abstract bool ConvertEmptyStringToNull { get; }
         public abstract string DataTypeName { get; }
         public abstract string Description { get; }
         public abstract string DisplayFormatString { get; }
         public abstract string DisplayName { get; }
         public abstract string EditFormatString { get; }
-        public abstract Microsoft.AspNetCore.Mvc.ModelBinding.ModelMetadata ElementMetadata { get; }
+        public abstract Microsoft.AspNetCore.Mvc.ModelBinding.ModelMetadata? ElementMetadata { get; }
-        public System.Type ElementType { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
+        public System.Type? ElementType { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
         public abstract System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<Microsoft.AspNetCore.Mvc.ModelBinding.EnumGroupAndName, string>> EnumGroupedDisplayNamesAndValues { get; }
         public abstract System.Collections.Generic.IReadOnlyDictionary<string, string> EnumNamesAndValues { get; }
         public abstract bool HasNonDefaultEditFormat { get; }
@@ -671,17 +672,17 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         public Microsoft.AspNetCore.Mvc.ModelBinding.Metadata.ModelMetadataKind MetadataKind { get { throw null; } }
         public abstract Microsoft.AspNetCore.Mvc.ModelBinding.Metadata.ModelBindingMessageProvider ModelBindingMessageProvider { get; }
         public System.Type ModelType { get { throw null; } }
-        public string Name { get { throw null; } }
+        public string? Name { get { throw null; } }
         public abstract string NullDisplayText { get; }
         public abstract int Order { get; }
-        public string ParameterName { get { throw null; } }
+        public string? ParameterName { get { throw null; } }
         public abstract string Placeholder { get; }
         public abstract Microsoft.AspNetCore.Mvc.ModelBinding.ModelPropertyCollection Properties { get; }
         public abstract Microsoft.AspNetCore.Mvc.ModelBinding.IPropertyFilterProvider PropertyFilterProvider { get; }
         public abstract System.Func<object, object> PropertyGetter { get; }
-        public string PropertyName { get { throw null; } }
+        public string? PropertyName { get { throw null; } }
         public abstract System.Action<object, object> PropertySetter { get; }
-        public virtual Microsoft.AspNetCore.Mvc.ModelBinding.Validation.IPropertyValidationFilter PropertyValidationFilter { get { throw null; } }
+        public virtual Microsoft.AspNetCore.Mvc.ModelBinding.Validation.IPropertyValidationFilter? PropertyValidationFilter { get { throw null; } }
         public abstract bool ShowForDisplay { get; }
         public abstract bool ShowForEdit { get; }
         public abstract string SimpleDisplayProperty { get; }
@@ -689,8 +690,8 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         public System.Type UnderlyingOrModelType { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
         public abstract bool ValidateChildren { get; }
         public abstract System.Collections.Generic.IReadOnlyList<object> ValidatorMetadata { get; }
-        public bool Equals(Microsoft.AspNetCore.Mvc.ModelBinding.ModelMetadata other) { throw null; }
+        public bool Equals(Microsoft.AspNetCore.Mvc.ModelBinding.ModelMetadata? other) { throw null; }
-        public override bool Equals(object obj) { throw null; }
+        public override bool Equals(object? obj) { throw null; }
         public string GetDisplayName() { throw null; }
         public override int GetHashCode() { throw null; }
         public virtual System.Collections.Generic.IEnumerable<Microsoft.AspNetCore.Mvc.ModelBinding.ModelMetadata> GetMetadataForProperties(System.Type modelType) { throw null; }
@@ -708,7 +709,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
     public partial class ModelPropertyCollection : System.Collections.ObjectModel.ReadOnlyCollection<Microsoft.AspNetCore.Mvc.ModelBinding.ModelMetadata>
     {
         public ModelPropertyCollection(System.Collections.Generic.IEnumerable<Microsoft.AspNetCore.Mvc.ModelBinding.ModelMetadata> properties) : base (default(System.Collections.Generic.IList<Microsoft.AspNetCore.Mvc.ModelBinding.ModelMetadata>)) { }
-        public Microsoft.AspNetCore.Mvc.ModelBinding.ModelMetadata this[string propertyName] { get { throw null; } }
+        public Microsoft.AspNetCore.Mvc.ModelBinding.ModelMetadata? this[string propertyName] { get { throw null; } }
     }
     public partial class ModelStateDictionary : System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string, Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateEntry>>, System.Collections.Generic.IReadOnlyCollection<System.Collections.Generic.KeyValuePair<string, Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateEntry>>, System.Collections.Generic.IReadOnlyDictionary<string, Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateEntry>, System.Collections.IEnumerable
     {
@@ -724,8 +725,8 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         public Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateDictionary.KeyEnumerable Keys { get { throw null; } }
         public int MaxAllowedErrors { get { throw null; } set { } }
         public Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateEntry Root { get { throw null; } }
-        System.Collections.Generic.IEnumerable<string> System.Collections.Generic.IReadOnlyDictionary<System.String,Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateEntry>.Keys { get { throw null; } }
+        System.Collections.Generic.IEnumerable<string> System.Collections.Generic.IReadOnlyDictionary<string, Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateEntry>.Keys { get { throw null; } }
-        System.Collections.Generic.IEnumerable<Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateEntry> System.Collections.Generic.IReadOnlyDictionary<System.String,Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateEntry>.Values { get { throw null; } }
+        System.Collections.Generic.IEnumerable<Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateEntry> System.Collections.Generic.IReadOnlyDictionary<string, Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateEntry>.Values { get { throw null; } }
         public Microsoft.AspNetCore.Mvc.ModelBinding.ModelValidationState ValidationState { get { throw null; } }
         public Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateDictionary.ValueEnumerable Values { get { throw null; } }
         public void AddModelError(string key, System.Exception exception, Microsoft.AspNetCore.Mvc.ModelBinding.ModelMetadata metadata) { }
@@ -742,14 +743,14 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         public void Merge(Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateDictionary dictionary) { }
         public bool Remove(string key) { throw null; }
         public void SetModelValue(string key, Microsoft.AspNetCore.Mvc.ModelBinding.ValueProviderResult valueProviderResult) { }
-        public void SetModelValue(string key, object rawValue, string attemptedValue) { }
+        public void SetModelValue(string key, object? rawValue, string attemptedValue) { }
         public static bool StartsWithPrefix(string prefix, string key) { throw null; }
-        System.Collections.Generic.IEnumerator<System.Collections.Generic.KeyValuePair<string, Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateEntry>> System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<System.String,Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateEntry>>.GetEnumerator() { throw null; }
+        System.Collections.Generic.IEnumerator<System.Collections.Generic.KeyValuePair<string, Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateEntry>> System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string, Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateEntry>>.GetEnumerator() { throw null; }
         System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() { throw null; }
         public bool TryAddModelError(string key, System.Exception exception, Microsoft.AspNetCore.Mvc.ModelBinding.ModelMetadata metadata) { throw null; }
         public bool TryAddModelError(string key, string errorMessage) { throw null; }
         public bool TryAddModelException(string key, System.Exception exception) { throw null; }
-        public bool TryGetValue(string key, out Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateEntry value) { throw null; }
+        public bool TryGetValue(string key, [System.Diagnostics.CodeAnalysis.NotNullWhenAttribute(true)] out Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateEntry? value) { throw null; }
         [System.Runtime.InteropServices.StructLayoutAttribute(System.Runtime.InteropServices.LayoutKind.Sequential)]
         public partial struct Enumerator : System.Collections.Generic.IEnumerator<System.Collections.Generic.KeyValuePair<string, Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateEntry>>, System.Collections.IEnumerator, System.IDisposable
         {
@@ -769,7 +770,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
             private readonly int _dummyPrimitive;
             public KeyEnumerable(Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateDictionary dictionary) { throw null; }
             public Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateDictionary.KeyEnumerator GetEnumerator() { throw null; }
-            System.Collections.Generic.IEnumerator<string> System.Collections.Generic.IEnumerable<System.String>.GetEnumerator() { throw null; }
+            System.Collections.Generic.IEnumerator<string> System.Collections.Generic.IEnumerable<string>.GetEnumerator() { throw null; }
             System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() { throw null; }
         }
         [System.Runtime.InteropServices.StructLayoutAttribute(System.Runtime.InteropServices.LayoutKind.Sequential)]
@@ -791,7 +792,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
             private readonly int _dummyPrimitive;
             public PrefixEnumerable(Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateDictionary dictionary, string prefix) { throw null; }
             public Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateDictionary.Enumerator GetEnumerator() { throw null; }
-            System.Collections.Generic.IEnumerator<System.Collections.Generic.KeyValuePair<string, Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateEntry>> System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<System.String,Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateEntry>>.GetEnumerator() { throw null; }
+            System.Collections.Generic.IEnumerator<System.Collections.Generic.KeyValuePair<string, Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateEntry>> System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<string, Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateEntry>>.GetEnumerator() { throw null; }
             System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() { throw null; }
         }
         [System.Runtime.InteropServices.StructLayoutAttribute(System.Runtime.InteropServices.LayoutKind.Sequential)]
@@ -820,13 +821,13 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
     public abstract partial class ModelStateEntry
     {
         protected ModelStateEntry() { }
-        public string AttemptedValue { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public string? AttemptedValue { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
-        public abstract System.Collections.Generic.IReadOnlyList<Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateEntry> Children { get; }
+        public abstract System.Collections.Generic.IReadOnlyList<Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateEntry>? Children { get; }
         public Microsoft.AspNetCore.Mvc.ModelBinding.ModelErrorCollection Errors { get { throw null; } }
         public abstract bool IsContainerNode { get; }
-        public object RawValue { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public object? RawValue { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
         public Microsoft.AspNetCore.Mvc.ModelBinding.ModelValidationState ValidationState { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
-        public abstract Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateEntry GetModelStateForProperty(string propertyName);
+        public abstract Microsoft.AspNetCore.Mvc.ModelBinding.ModelStateEntry? GetModelStateForProperty(string propertyName);
     }
     public enum ModelValidationState
     {
@@ -859,11 +860,11 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         public ValueProviderResult(Microsoft.Extensions.Primitives.StringValues values) { throw null; }
         public ValueProviderResult(Microsoft.Extensions.Primitives.StringValues values, System.Globalization.CultureInfo culture) { throw null; }
         public System.Globalization.CultureInfo Culture { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
-        public string FirstValue { get { throw null; } }
+        public string? FirstValue { get { throw null; } }
         public int Length { get { throw null; } }
         public Microsoft.Extensions.Primitives.StringValues Values { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
         public bool Equals(Microsoft.AspNetCore.Mvc.ModelBinding.ValueProviderResult other) { throw null; }
-        public override bool Equals(object obj) { throw null; }
+        public override bool Equals(object? obj) { throw null; }
         public System.Collections.Generic.IEnumerator<string> GetEnumerator() { throw null; }
         public override int GetHashCode() { throw null; }
         public static bool operator ==(Microsoft.AspNetCore.Mvc.ModelBinding.ValueProviderResult x, Microsoft.AspNetCore.Mvc.ModelBinding.ValueProviderResult y) { throw null; }
@@ -896,14 +897,14 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Metadata
     {
         private readonly object _dummy;
         private readonly int _dummyPrimitive;
-        public System.Type ContainerType { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
+        public System.Type? ContainerType { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
         public Microsoft.AspNetCore.Mvc.ModelBinding.Metadata.ModelMetadataKind MetadataKind { get { throw null; } }
         public System.Type ModelType { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
-        public string Name { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
+        public string? Name { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
-        public System.Reflection.ParameterInfo ParameterInfo { get { throw null; } }
+        public System.Reflection.ParameterInfo? ParameterInfo { get { throw null; } }
-        public System.Reflection.PropertyInfo PropertyInfo { get { throw null; } }
+        public System.Reflection.PropertyInfo? PropertyInfo { get { throw null; } }
         public bool Equals(Microsoft.AspNetCore.Mvc.ModelBinding.Metadata.ModelMetadataIdentity other) { throw null; }
-        public override bool Equals(object obj) { throw null; }
+        public override bool Equals(object? obj) { throw null; }
         public static Microsoft.AspNetCore.Mvc.ModelBinding.Metadata.ModelMetadataIdentity ForParameter(System.Reflection.ParameterInfo parameter) { throw null; }
         public static Microsoft.AspNetCore.Mvc.ModelBinding.Metadata.ModelMetadataIdentity ForParameter(System.Reflection.ParameterInfo parameter, System.Type modelType) { throw null; }
         public static Microsoft.AspNetCore.Mvc.ModelBinding.Metadata.ModelMetadataIdentity ForProperty(System.Reflection.PropertyInfo propertyInfo, System.Type modelType, System.Type containerType) { throw null; }
@@ -1000,17 +1001,19 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Validation
         public ValidationEntry(Microsoft.AspNetCore.Mvc.ModelBinding.ModelMetadata metadata, string key, object model) { throw null; }
         public string Key { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
         public Microsoft.AspNetCore.Mvc.ModelBinding.ModelMetadata Metadata { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
-        public object Model { get { throw null; } }
+        public object? Model { get { throw null; } }
     }
     public partial class ValidationStateDictionary : System.Collections.Generic.ICollection<System.Collections.Generic.KeyValuePair<object, Microsoft.AspNetCore.Mvc.ModelBinding.Validation.ValidationStateEntry>>, System.Collections.Generic.IDictionary<object, Microsoft.AspNetCore.Mvc.ModelBinding.Validation.ValidationStateEntry>, System.Collections.Generic.IEnumerable<System.Collections.Generic.KeyValuePair<object, Microsoft.AspNetCore.Mvc.ModelBinding.Validation.ValidationStateEntry>>, System.Collections.Generic.IReadOnlyCollection<System.Collections.Generic.KeyValuePair<object, Microsoft.AspNetCore.Mvc.ModelBinding.Validation.ValidationStateEntry>>, System.Collections.Generic.IReadOnlyDictionary<object, Microsoft.AspNetCore.Mvc.ModelBinding.Validation.ValidationStateEntry>, System.Collections.IEnumerable
     {
         public ValidationStateDictionary() { }
         public int Count { get { throw null; } }
         public bool IsReadOnly { get { throw null; } }
-        public Microsoft.AspNetCore.Mvc.ModelBinding.Validation.ValidationStateEntry this[object key] { get { throw null; } set { } }
+        public Microsoft.AspNetCore.Mvc.ModelBinding.Validation.ValidationStateEntry? this[object key] { get { throw null; } set { } }
         public System.Collections.Generic.ICollection<object> Keys { get { throw null; } }
-        System.Collections.Generic.IEnumerable<object> System.Collections.Generic.IReadOnlyDictionary<System.Object,Microsoft.AspNetCore.Mvc.ModelBinding.Validation.ValidationStateEntry>.Keys { get { throw null; } }
+        Microsoft.AspNetCore.Mvc.ModelBinding.Validation.ValidationStateEntry System.Collections.Generic.IDictionary<object, Microsoft.AspNetCore.Mvc.ModelBinding.Validation.ValidationStateEntry>.this[object key] { get { throw null; } set { } }
-        System.Collections.Generic.IEnumerable<Microsoft.AspNetCore.Mvc.ModelBinding.Validation.ValidationStateEntry> System.Collections.Generic.IReadOnlyDictionary<System.Object,Microsoft.AspNetCore.Mvc.ModelBinding.Validation.ValidationStateEntry>.Values { get { throw null; } }
+        Microsoft.AspNetCore.Mvc.ModelBinding.Validation.ValidationStateEntry System.Collections.Generic.IReadOnlyDictionary<object, Microsoft.AspNetCore.Mvc.ModelBinding.Validation.ValidationStateEntry>.this[object key] { get { throw null; } }
+        System.Collections.Generic.IEnumerable<object> System.Collections.Generic.IReadOnlyDictionary<object, Microsoft.AspNetCore.Mvc.ModelBinding.Validation.ValidationStateEntry>.Keys { get { throw null; } }
+        System.Collections.Generic.IEnumerable<Microsoft.AspNetCore.Mvc.ModelBinding.Validation.ValidationStateEntry> System.Collections.Generic.IReadOnlyDictionary<object, Microsoft.AspNetCore.Mvc.ModelBinding.Validation.ValidationStateEntry>.Values { get { throw null; } }
         public System.Collections.Generic.ICollection<Microsoft.AspNetCore.Mvc.ModelBinding.Validation.ValidationStateEntry> Values { get { throw null; } }
         public void Add(System.Collections.Generic.KeyValuePair<object, Microsoft.AspNetCore.Mvc.ModelBinding.Validation.ValidationStateEntry> item) { }
         public void Add(object key, Microsoft.AspNetCore.Mvc.ModelBinding.Validation.ValidationStateEntry value) { }
@@ -1022,7 +1025,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Validation
         public bool Remove(System.Collections.Generic.KeyValuePair<object, Microsoft.AspNetCore.Mvc.ModelBinding.Validation.ValidationStateEntry> item) { throw null; }
         public bool Remove(object key) { throw null; }
         System.Collections.IEnumerator System.Collections.IEnumerable.GetEnumerator() { throw null; }
-        public bool TryGetValue(object key, out Microsoft.AspNetCore.Mvc.ModelBinding.Validation.ValidationStateEntry value) { throw null; }
+        public bool TryGetValue(object key, [System.Diagnostics.CodeAnalysis.MaybeNullWhenAttribute(false)] out Microsoft.AspNetCore.Mvc.ModelBinding.Validation.ValidationStateEntry value) { throw null; }
     }
     public partial class ValidationStateEntry
     {
@@ -1050,25 +1053,25 @@ namespace Microsoft.AspNetCore.Mvc.Routing
         public int Order { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
         public bool SuppressLinkGeneration { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
         public bool SuppressPathMatching { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
-        public string Template { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public string? Template { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
     }
     public partial class UrlActionContext
     {
         public UrlActionContext() { }
-        public string Action { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public string? Action { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
-        public string Controller { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public string? Controller { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
-        public string Fragment { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public string? Fragment { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
-        public string Host { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public string? Host { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
-        public string Protocol { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public string? Protocol { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
-        public object Values { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public object? Values { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
     }
     public partial class UrlRouteContext
     {
         public UrlRouteContext() { }
-        public string Fragment { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public string? Fragment { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
-        public string Host { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public string? Host { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
-        public string Protocol { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public string? Protocol { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
-        public string RouteName { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public string? RouteName { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
-        public object Values { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
+        public object? Values { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } [System.Runtime.CompilerServices.CompilerGeneratedAttribute] set { } }
     }
 }

src/Mvc/Mvc.Abstractions/src/Abstractions/ActionDescriptor.cs

@@ -38,42 +38,42 @@ namespace Microsoft.AspNetCore.Mvc.Abstractions
         /// <summary>
         /// Gets or sets the <see cref="Routing.AttributeRouteInfo"/>.
         /// </summary>
-        public AttributeRouteInfo AttributeRouteInfo { get; set; }
+        public AttributeRouteInfo? AttributeRouteInfo { get; set; }
 
         /// <summary>
         /// The set of constraints for this action. Must all be satisfied for the action to be selected.
         /// </summary>
-        public IList<IActionConstraintMetadata> ActionConstraints { get; set; }
+        public IList<IActionConstraintMetadata>? ActionConstraints { get; set; }
 
         /// <summary>
         /// Gets or sets the endpoint metadata for this action.
         /// This API is meant for infrastructure and should not be used by application code.
         /// </summary>
-        public IList<object> EndpointMetadata { get; set; }
+        public IList<object> EndpointMetadata { get; set; } = Array.Empty<ParameterDescriptor>();
 
         /// <summary>
         /// The set of parameters associated with this action.
         /// </summary>
-        public IList<ParameterDescriptor> Parameters { get; set; }
+        public IList<ParameterDescriptor> Parameters { get; set; } = Array.Empty<ParameterDescriptor>();
 
         /// <summary>
         /// The set of properties which are model bound.
         /// </summary>
-        public IList<ParameterDescriptor> BoundProperties { get; set; }
+        public IList<ParameterDescriptor> BoundProperties { get; set; } = Array.Empty<ParameterDescriptor>();
 
         /// <summary>
         /// The set of filters associated with this action.
         /// </summary>
-        public IList<FilterDescriptor> FilterDescriptors { get; set; }
+        public IList<FilterDescriptor> FilterDescriptors { get; set; } = Array.Empty<FilterDescriptor>();
 
         /// <summary>
         /// A friendly name for this action.
         /// </summary>
-        public virtual string DisplayName { get; set; }
+        public virtual string? DisplayName { get; set; }
 
         /// <summary>
         /// Stores arbitrary metadata properties associated with the <see cref="ActionDescriptor"/>.
         /// </summary>
-        public IDictionary<object, object> Properties { get; set; }
+        public IDictionary<object, object> Properties { get; set; } = default!;
     }
 }

src/Mvc/Mvc.Abstractions/src/Abstractions/ActionDescriptorExtensions.cs

@@ -24,14 +24,13 @@ namespace Microsoft.AspNetCore.Mvc.Abstractions
                 throw new ArgumentNullException(nameof(actionDescriptor));
             }
 
-            object value;
+            if (actionDescriptor.Properties.TryGetValue(typeof(T), out var value))
-            if (actionDescriptor.Properties.TryGetValue(typeof(T), out value))
             {
                 return (T)value;
             }
             else
             {
-                return default(T);
+                return default!;
             }
         }
 

src/Mvc/Mvc.Abstractions/src/Abstractions/ActionInvokerProviderContext.cs

@@ -32,6 +32,6 @@ namespace Microsoft.AspNetCore.Mvc.Abstractions
         /// <summary>
         /// Gets or sets the <see cref="IActionInvoker"/> that will be used to invoke <see cref="ActionContext" />
         /// </summary>
-        public IActionInvoker Result { get; set; }
+        public IActionInvoker? Result { get; set; }
     }
 }

src/Mvc/Mvc.Abstractions/src/Abstractions/ParameterDescriptor.cs

@@ -14,16 +14,16 @@ namespace Microsoft.AspNetCore.Mvc.Abstractions
         /// <summary>
         /// Gets or sets the parameter name.
         /// </summary>
-        public string Name { get; set; }
+        public string Name { get; set; } = default!;
 
         /// <summary>
         /// Gets or sets the type of the parameter.
         /// </summary>
-        public Type ParameterType { get; set; }
+        public Type ParameterType { get; set; } = default!;
 
         /// <summary>
         /// Gets or sets the <see cref="ModelBinding.BindingInfo"/> for the parameter.
         /// </summary>
-        public BindingInfo BindingInfo { get; set; }
+        public BindingInfo BindingInfo { get; set; } = default!;
     }
 }

src/Mvc/Mvc.Abstractions/src/ActionConstraints/ActionConstraintContext.cs

@@ -1,6 +1,7 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System;
 using System.Collections.Generic;
 using Microsoft.AspNetCore.Routing;
 
@@ -15,16 +16,16 @@ namespace Microsoft.AspNetCore.Mvc.ActionConstraints
         /// The list of <see cref="ActionSelectorCandidate"/>. This includes all actions that are valid for the current
         /// request, as well as their constraints.
         /// </summary>
-        public IReadOnlyList<ActionSelectorCandidate> Candidates { get; set; }
+        public IReadOnlyList<ActionSelectorCandidate> Candidates { get; set; } = Array.Empty<ActionSelectorCandidate>();
 
         /// <summary>
         /// The current <see cref="ActionSelectorCandidate"/>.
         /// </summary>
-        public ActionSelectorCandidate CurrentCandidate { get; set; }
+        public ActionSelectorCandidate CurrentCandidate { get; set; } = default!;
 
         /// <summary>
         /// The <see cref="RouteContext"/>.
         /// </summary>
-        public RouteContext RouteContext { get; set; }
+        public RouteContext RouteContext { get; set; } = default!;
     }
 }

src/Mvc/Mvc.Abstractions/src/ActionConstraints/ActionConstraintItem.cs

@@ -28,7 +28,7 @@ namespace Microsoft.AspNetCore.Mvc.ActionConstraints
         /// <summary>
         /// The <see cref="IActionConstraint"/> associated with <see cref="Metadata"/>.
         /// </summary>
-        public IActionConstraint Constraint { get; set; }
+        public IActionConstraint Constraint { get; set; } = default!;
 
         /// <summary>
         /// The <see cref="IActionConstraintMetadata"/> instance.

src/Mvc/Mvc.Abstractions/src/ActionContext.cs

@@ -31,10 +31,10 @@ namespace Microsoft.AspNetCore.Mvc
         /// <param name="actionContext">The <see cref="ActionContext"/> to copy.</param>
         public ActionContext(ActionContext actionContext)
             : this(
-                actionContext?.HttpContext,
+                actionContext.HttpContext,
-                actionContext?.RouteData,
+                actionContext.RouteData,
-                actionContext?.ActionDescriptor,
+                actionContext.ActionDescriptor,
-                actionContext?.ModelState)
+                actionContext.ModelState)
         {
         }
 
@@ -97,10 +97,7 @@ namespace Microsoft.AspNetCore.Mvc
         /// <remarks>
         /// The property setter is provided for unit test purposes only.
         /// </remarks>
-        public ActionDescriptor ActionDescriptor
+        public ActionDescriptor ActionDescriptor { get; set; } = default!;
-        {
-            get; set;
-        }
 
         /// <summary>
         /// Gets or sets the <see cref="Http.HttpContext"/> for the current request.
@@ -108,18 +105,12 @@ namespace Microsoft.AspNetCore.Mvc
         /// <remarks>
         /// The property setter is provided for unit test purposes only.
         /// </remarks>
-        public HttpContext HttpContext
+        public HttpContext HttpContext { get; set; } = default!;
-        {
-            get; set;
-        }
 
         /// <summary>
         /// Gets the <see cref="ModelStateDictionary"/>.
         /// </summary>
-        public ModelStateDictionary ModelState
+        public ModelStateDictionary ModelState { get; } = default!;
-        {
-            get;
-        }
 
         /// <summary>
         /// Gets or sets the <see cref="AspNetCore.Routing.RouteData"/> for the current request.
@@ -127,9 +118,6 @@ namespace Microsoft.AspNetCore.Mvc
         /// <remarks>
         /// The property setter is provided for unit test purposes only.
         /// </remarks>
-        public RouteData RouteData
+        public RouteData RouteData { get; set; } = default!;
-        {
-            get; set;
-        }
     }
 }

src/Mvc/Mvc.Abstractions/src/ApiExplorer/ApiDescription.cs

@@ -16,17 +16,17 @@ namespace Microsoft.AspNetCore.Mvc.ApiExplorer
         /// <summary>
         /// Gets or sets <see cref="ActionDescriptor"/> for this api.
         /// </summary>
-        public ActionDescriptor ActionDescriptor { get; set; }
+        public ActionDescriptor ActionDescriptor { get; set; } = default!;
 
         /// <summary>
         /// Gets or sets group name for this api.
         /// </summary>
-        public string GroupName { get; set; }
+        public string? GroupName { get; set; }
 
         /// <summary>
         /// Gets or sets the supported HTTP method for this api, or null if all HTTP methods are supported.
         /// </summary>
-        public string HttpMethod { get; set; }
+        public string? HttpMethod { get; set; }
 
         /// <summary>
         /// Gets a list of <see cref="ApiParameterDescription"/> for this api.
@@ -41,7 +41,7 @@ namespace Microsoft.AspNetCore.Mvc.ApiExplorer
         /// <summary>
         /// Gets or sets relative url path template (relative to application root) for this api.
         /// </summary>
-        public string RelativePath { get; set; }
+        public string RelativePath { get; set; } = default!;
 
         /// <summary>
         /// Gets the list of possible formats for a request.

src/Mvc/Mvc.Abstractions/src/ApiExplorer/ApiParameterDescription.cs

@@ -15,37 +15,37 @@ namespace Microsoft.AspNetCore.Mvc.ApiExplorer
         /// <summary>
         /// Gets or sets the <see cref="ModelMetadata"/>.
         /// </summary>
-        public ModelMetadata ModelMetadata { get; set; }
+        public ModelMetadata ModelMetadata { get; set; } = default!;
 
         /// <summary>
         /// Gets or sets the name.
         /// </summary>
-        public string Name { get; set; }
+        public string Name { get; set; } = default!;
 
         /// <summary>
         /// Gets or sets the <see cref="ApiParameterRouteInfo"/>.
         /// </summary>
-        public ApiParameterRouteInfo RouteInfo { get; set; }
+        public ApiParameterRouteInfo? RouteInfo { get; set; }
 
         /// <summary>
         /// Gets or sets the <see cref="BindingSource"/>.
         /// </summary>
-        public BindingSource Source { get; set; }
+        public BindingSource Source { get; set; } = default!;
 
         /// <summary>
         /// Gets or sets the <see cref="BindingInfo"/>.
         /// </summary>
-        public BindingInfo BindingInfo { get; set; }
+        public BindingInfo? BindingInfo { get; set; }
 
         /// <summary>
         /// Gets or sets the parameter type.
         /// </summary>
-        public Type Type { get; set; }
+        public Type Type { get; set; } = default!;
 
         /// <summary>
         /// Gets or sets the parameter descriptor.
         /// </summary>
-        public ParameterDescriptor ParameterDescriptor { get; set; }
+        public ParameterDescriptor ParameterDescriptor { get; set; } = default!;
 
         /// <summary>
         /// Gets or sets a value that determines if the parameter is required.
@@ -63,6 +63,6 @@ namespace Microsoft.AspNetCore.Mvc.ApiExplorer
         /// <summary>
         /// Gets or sets the default value for a parameter.
         /// </summary>
-        public object DefaultValue { get; set; }
+        public object? DefaultValue { get; set; }
     }
 }

src/Mvc/Mvc.Abstractions/src/ApiExplorer/ApiParameterRouteInfo.cs

@@ -18,12 +18,12 @@ namespace Microsoft.AspNetCore.Mvc.ApiExplorer
         /// Route constraints are only applied when a value is bound from a URL's path. See
         /// <see cref="ApiParameterDescription.Source"/> for the data source considered.
         /// </remarks>
-        public IEnumerable<IRouteConstraint> Constraints { get; set; }
+        public IEnumerable<IRouteConstraint>? Constraints { get; set; }
 
         /// <summary>
         /// Gets or sets the default value for the parameter.
         /// </summary>
-        public object DefaultValue { get; set; }
+        public object? DefaultValue { get; set; }
 
         /// <summary>
         /// Gets a value indicating whether not a parameter is considered optional by routing.

src/Mvc/Mvc.Abstractions/src/ApiExplorer/ApiRequestFormat.cs

@@ -13,11 +13,11 @@ namespace Microsoft.AspNetCore.Mvc.ApiExplorer
         /// <summary>
         /// The formatter used to read this request.
         /// </summary>
-        public IInputFormatter Formatter { get; set; }
+        public IInputFormatter Formatter { get; set; } = default!;
 
         /// <summary>
         /// The media type of the request.
         /// </summary>
-        public string MediaType { get; set; }
+        public string MediaType { get; set; } = default!;
     }
 }

src/Mvc/Mvc.Abstractions/src/ApiExplorer/ApiResponseFormat.cs

@@ -13,11 +13,11 @@ namespace Microsoft.AspNetCore.Mvc.ApiExplorer
         /// <summary>
         /// Gets or sets the formatter used to output this response.
         /// </summary>
-        public IOutputFormatter Formatter { get; set; }
+        public IOutputFormatter Formatter { get; set; } = default!;
 
         /// <summary>
         /// Gets or sets the media type of the response.
         /// </summary>
-        public string MediaType { get; set; }
+        public string MediaType { get; set; } = default!;
     }
 }

src/Mvc/Mvc.Abstractions/src/ApiExplorer/ApiResponseType.cs

@@ -23,7 +23,7 @@ namespace Microsoft.AspNetCore.Mvc.ApiExplorer
         /// <remarks>
         /// Will be null if <see cref="Type"/> is null or void.
         /// </remarks>
-        public ModelMetadata ModelMetadata { get; set; }
+        public ModelMetadata? ModelMetadata { get; set; }
 
         /// <summary>
         /// Gets or sets the CLR data type of the response or null.
@@ -33,7 +33,7 @@ namespace Microsoft.AspNetCore.Mvc.ApiExplorer
         /// <c>Microsoft.AspNetCore.Mvc.ProducesAttribute</c> or <c>Microsoft.AspNetCore.Mvc.ProducesResponseTypeAttribute</c> on an action method
         /// to specify a response type.
         /// </remarks>
-        public Type Type { get; set; }
+        public Type? Type { get; set; }
 
         /// <summary>
         /// Gets or sets the HTTP response status code.

src/Mvc/Mvc.Abstractions/src/Filters/ActionExecutedContext.cs

@@ -12,8 +12,8 @@ namespace Microsoft.AspNetCore.Mvc.Filters
     /// </summary>
     public class ActionExecutedContext : FilterContext
     {
-        private Exception _exception;
+        private Exception? _exception;
-        private ExceptionDispatchInfo _exceptionDispatchInfo;
+        private ExceptionDispatchInfo? _exceptionDispatchInfo;
 
         /// <summary>
         /// Instantiates a new <see cref="ActionExecutingContext"/> instance.
@@ -44,7 +44,7 @@ namespace Microsoft.AspNetCore.Mvc.Filters
         /// Gets or sets the <see cref="System.Exception"/> caught while executing the action or action filters, if
         /// any.
         /// </summary>
-        public virtual Exception Exception
+        public virtual Exception? Exception
         {
             get
             {
@@ -69,7 +69,7 @@ namespace Microsoft.AspNetCore.Mvc.Filters
         /// Gets or sets the <see cref="System.Runtime.ExceptionServices.ExceptionDispatchInfo"/> for the
         /// <see cref="Exception"/>, if an <see cref="System.Exception"/> was caught and this information captured.
         /// </summary>
-        public virtual ExceptionDispatchInfo ExceptionDispatchInfo
+        public virtual ExceptionDispatchInfo? ExceptionDispatchInfo
         {
             get
             {
@@ -91,6 +91,6 @@ namespace Microsoft.AspNetCore.Mvc.Filters
         /// <summary>
         /// Gets or sets the <see cref="IActionResult"/>.
         /// </summary>
-        public virtual IActionResult Result { get; set; }
+        public virtual IActionResult Result { get; set; } = default!;
     }
 }

src/Mvc/Mvc.Abstractions/src/Filters/ActionExecutingContext.cs

@@ -41,7 +41,7 @@ namespace Microsoft.AspNetCore.Mvc.Filters
         /// Gets or sets the <see cref="IActionResult"/> to execute. Setting <see cref="Result"/> to a non-<c>null</c>
         /// value inside an action filter will short-circuit the action and any remaining action filters.
         /// </summary>
-        public virtual IActionResult Result { get; set; }
+        public virtual IActionResult? Result { get; set; }
 
         /// <summary>
         /// Gets the arguments to pass when invoking the action. Keys are parameter names.

src/Mvc/Mvc.Abstractions/src/Filters/AuthorizationFilterContext.cs

@@ -27,6 +27,6 @@ namespace Microsoft.AspNetCore.Mvc.Filters
         /// Gets or sets the result of the request. Setting <see cref="Result"/> to a non-<c>null</c> value inside
         /// an authorization filter will short-circuit the remainder of the filter pipeline.
         /// </summary>
-        public virtual IActionResult Result { get; set; }
+        public virtual IActionResult? Result { get; set; }
     }
 }

src/Mvc/Mvc.Abstractions/src/Filters/ExceptionContext.cs

@@ -13,8 +13,8 @@ namespace Microsoft.AspNetCore.Mvc.Filters
     /// </summary>
     public class ExceptionContext : FilterContext
     {
-        private Exception _exception;
+        private Exception? _exception;
-        private ExceptionDispatchInfo _exceptionDispatchInfo;
+        private ExceptionDispatchInfo? _exceptionDispatchInfo;
 
         /// <summary>
         /// Instantiates a new <see cref="ExceptionContext"/> instance.
@@ -39,7 +39,7 @@ namespace Microsoft.AspNetCore.Mvc.Filters
                 }
                 else
                 {
-                    return _exception;
+                    return _exception!;
                 }
             }
 
@@ -54,7 +54,7 @@ namespace Microsoft.AspNetCore.Mvc.Filters
         /// Gets or sets the <see cref="System.Runtime.ExceptionServices.ExceptionDispatchInfo"/> for the
         /// <see cref="Exception"/>, if this information was captured.
         /// </summary>
-        public virtual ExceptionDispatchInfo ExceptionDispatchInfo
+        public virtual ExceptionDispatchInfo? ExceptionDispatchInfo
         {
             get
             {
@@ -76,6 +76,6 @@ namespace Microsoft.AspNetCore.Mvc.Filters
         /// <summary>
         /// Gets or sets the <see cref="IActionResult"/>.
         /// </summary>
-        public virtual IActionResult Result { get; set; }
+        public virtual IActionResult? Result { get; set; }
     }
 }

src/Mvc/Mvc.Abstractions/src/Filters/FilterContext.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Diagnostics.CodeAnalysis;
 
 namespace Microsoft.AspNetCore.Mvc.Filters
 {
@@ -81,6 +82,7 @@ namespace Microsoft.AspNetCore.Mvc.Filters
         /// <returns>The implementation of <typeparamref name="TMetadata"/> applied to the action associated with
         /// the <see cref="FilterContext"/>
         /// </returns>
+        [return: MaybeNull]
         public TMetadata FindEffectivePolicy<TMetadata>() where TMetadata : IFilterMetadata
         {
             // The most specific policy is the one closest to the action (nearest the end of the list).
@@ -93,7 +95,7 @@ namespace Microsoft.AspNetCore.Mvc.Filters
                 }
             }
 
-            return default(TMetadata);
+            return default;
         }
     }
 }

src/Mvc/Mvc.Abstractions/src/Filters/FilterItem.cs

@@ -48,12 +48,12 @@ namespace Microsoft.AspNetCore.Mvc.Filters
         /// <summary>
         /// Gets the <see cref="FilterDescriptor"/> containing the filter metadata.
         /// </summary>
-        public FilterDescriptor Descriptor { get; }
+        public FilterDescriptor Descriptor { get; } = default!;
 
         /// <summary>
         /// Gets or sets the executable <see cref="IFilterMetadata"/> associated with <see cref="Descriptor"/>.
         /// </summary>
-        public IFilterMetadata Filter { get; set; }
+        public IFilterMetadata Filter { get; set; } = default!;
 
         /// <summary>
         /// Gets or sets a value indicating whether or not <see cref="Filter"/> can be reused across requests.

src/Mvc/Mvc.Abstractions/src/Filters/ResourceExecutedContext.cs

@@ -12,8 +12,8 @@ namespace Microsoft.AspNetCore.Mvc.Filters
     /// </summary>
     public class ResourceExecutedContext : FilterContext
     {
-        private Exception _exception;
+        private Exception? _exception;
-        private ExceptionDispatchInfo _exceptionDispatchInfo;
+        private ExceptionDispatchInfo? _exceptionDispatchInfo;
 
         /// <summary>
         /// Creates a new <see cref="ResourceExecutedContext"/>.
@@ -44,7 +44,7 @@ namespace Microsoft.AspNetCore.Mvc.Filters
         /// Setting <see cref="ExceptionHandled"/> to <c>true</c> will also mark the exception as handled.
         /// </para>
         /// </remarks>
-        public virtual Exception Exception
+        public virtual Exception? Exception
         {
             get
             {
@@ -77,7 +77,7 @@ namespace Microsoft.AspNetCore.Mvc.Filters
         /// Setting <see cref="ExceptionHandled"/> to <c>true</c> will also mark the exception as handled.
         /// </para>
         /// </remarks>
-        public virtual ExceptionDispatchInfo ExceptionDispatchInfo
+        public virtual ExceptionDispatchInfo? ExceptionDispatchInfo
         {
             get
             {
@@ -115,6 +115,6 @@ namespace Microsoft.AspNetCore.Mvc.Filters
         /// to resource filters.
         /// </para>
         /// </remarks>
-        public virtual IActionResult Result { get; set; }
+        public virtual IActionResult? Result { get; set; }
     }
 }

src/Mvc/Mvc.Abstractions/src/Filters/ResourceExecutingContext.cs

@@ -40,7 +40,7 @@ namespace Microsoft.AspNetCore.Mvc.Filters
         /// Setting <see cref="Result"/> to a non-<c>null</c> value inside a resource filter will
         /// short-circuit execution of additional resource filters and the action itself.
         /// </remarks>
-        public virtual IActionResult Result { get; set; }
+        public virtual IActionResult? Result { get; set; }
 
         /// <summary>
         /// Gets the list of <see cref="IValueProviderFactory"/> instances used by model binding.

src/Mvc/Mvc.Abstractions/src/Filters/ResultExecutedContext.cs

@@ -12,8 +12,8 @@ namespace Microsoft.AspNetCore.Mvc.Filters
     /// </summary>
     public class ResultExecutedContext : FilterContext
     {
-        private Exception _exception;
+        private Exception? _exception;
-        private ExceptionDispatchInfo _exceptionDispatchInfo;
+        private ExceptionDispatchInfo? _exceptionDispatchInfo;
 
         /// <summary>
         /// Instantiates a new <see cref="ResultExecutedContext"/> instance.
@@ -55,7 +55,7 @@ namespace Microsoft.AspNetCore.Mvc.Filters
         /// Gets or sets the <see cref="System.Exception"/> caught while executing the result or result filters, if
         /// any.
         /// </summary>
-        public virtual Exception Exception
+        public virtual Exception? Exception
         {
             get
             {
@@ -80,7 +80,7 @@ namespace Microsoft.AspNetCore.Mvc.Filters
         /// Gets or sets the <see cref="System.Runtime.ExceptionServices.ExceptionDispatchInfo"/> for the
         /// <see cref="Exception"/>, if an <see cref="System.Exception"/> was caught and this information captured.
         /// </summary>
-        public virtual ExceptionDispatchInfo ExceptionDispatchInfo
+        public virtual ExceptionDispatchInfo? ExceptionDispatchInfo
         {
             get
             {

src/Mvc/Mvc.Abstractions/src/Formatters/FormatterCollection.cs

@@ -11,7 +11,7 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
     /// Represents a collection of formatters.
     /// </summary>
     /// <typeparam name="TFormatter">The type of formatters in the collection.</typeparam>
-    public class FormatterCollection<TFormatter> : Collection<TFormatter>
+    public class FormatterCollection<TFormatter> : Collection<TFormatter> where TFormatter : notnull
     {
         /// <summary>
         /// Initializes a new instance of the <see cref="FormatterCollection{TFormatter}"/> class that is empty.

src/Mvc/Mvc.Abstractions/src/Formatters/InputFormatterResult.cs

@@ -42,7 +42,7 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
         /// <value>
         /// <c>null</c> if <see cref="HasError"/> is <c>true</c>.
         /// </value>
-        public object Model { get; }
+        public object? Model { get; }
 
         /// <summary>
         /// Returns an <see cref="InputFormatterResult"/> indicating the <see cref="IInputFormatter.ReadAsync"/>

src/Mvc/Mvc.Abstractions/src/Formatters/OutputFormatterCanWriteContext.cs

@@ -53,11 +53,11 @@ namespace Microsoft.AspNetCore.Mvc.Formatters
         /// <summary>
         /// Gets or sets the object to write to the response.
         /// </summary>
-        public virtual object Object { get; protected set; }
+        public virtual object? Object { get; protected set; }
 
         /// <summary>
         /// Gets or sets the <see cref="Type"/> of the object to write to the response.
         /// </summary>
-        public virtual Type ObjectType { get; protected set; }
+        public virtual Type? ObjectType { get; protected set; }
     }
 }

src/Mvc/Mvc.Abstractions/src/Microsoft.AspNetCore.Mvc.Abstractions.csproj

@@ -9,6 +9,7 @@ Microsoft.AspNetCore.Mvc.IActionResult</Description>
     <GenerateDocumentationFile>true</GenerateDocumentationFile>
     <PackageTags>aspnetcore;aspnetcoremvc</PackageTags>
     <IsPackable>false</IsPackable>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>
@@ -20,8 +21,4 @@ Microsoft.AspNetCore.Mvc.IActionResult</Description>
     <Reference Include="Microsoft.Net.Http.Headers" />
   </ItemGroup>
 
-  <ItemGroup Label="Shared Source">
-    <Compile Include="$(SharedSourceRoot)HashCodeCombiner\*.cs" />
-  </ItemGroup>
-
 </Project>

src/Mvc/Mvc.Abstractions/src/ModelBinding/BindingInfo.cs

@@ -13,7 +13,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
     /// </summary>
     public class BindingInfo
     {
-        private Type _binderType;
+        private Type? _binderType;
 
         /// <summary>
         /// Creates a new <see cref="BindingInfo"/>.
@@ -44,12 +44,12 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// <summary>
         /// Gets or sets the <see cref="ModelBinding.BindingSource"/>.
         /// </summary>
-        public BindingSource BindingSource { get; set; }
+        public BindingSource? BindingSource { get; set; }
 
         /// <summary>
         /// Gets or sets the binder model name.
         /// </summary>
-        public string BinderModelName { get; set; }
+        public string? BinderModelName { get; set; }
 
         /// <summary>
         /// Gets or sets the <see cref="Type"/> of the <see cref="IModelBinder"/> implementation used to bind the
@@ -59,7 +59,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// Also set <see cref="BindingSource"/> if the specified <see cref="IModelBinder"/> implementation does not
         /// use values from form data, route values or the query string.
         /// </remarks>
-        public Type BinderType
+        public Type? BinderType
         {
             get => _binderType;
             set
@@ -80,13 +80,13 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// <summary>
         /// Gets or sets the <see cref="ModelBinding.IPropertyFilterProvider"/>.
         /// </summary>
-        public IPropertyFilterProvider PropertyFilterProvider { get; set; }
+        public IPropertyFilterProvider? PropertyFilterProvider { get; set; }
 
         /// <summary>
         /// Gets or sets a predicate which determines whether or not the model should be bound based on state
         /// from the current request.
         /// </summary>
-        public Func<ActionContext, bool> RequestPredicate { get; set; }
+        public Func<ActionContext, bool>? RequestPredicate { get; set; }
 
         /// <summary>
         /// Gets or sets the value which decides if empty bodies are treated as valid inputs.
@@ -104,7 +104,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// <param name="attributes">A collection of attributes which are used to construct <see cref="BindingInfo"/>
         /// </param>
         /// <returns>A new instance of <see cref="BindingInfo"/>.</returns>
-        public static BindingInfo GetBindingInfo(IEnumerable<object> attributes)
+        public static BindingInfo? GetBindingInfo(IEnumerable<object> attributes)
         {
             var bindingInfo = new BindingInfo();
             var isBindingInfoPresent = false;
@@ -182,7 +182,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// <param name="attributes">A collection of attributes which are used to construct <see cref="BindingInfo"/>.</param>
         /// <param name="modelMetadata">The <see cref="ModelMetadata"/>.</param>
         /// <returns>A new instance of <see cref="BindingInfo"/> if any binding metadata was discovered; otherwise or <see langword="null"/>.</returns>
-        public static BindingInfo GetBindingInfo(IEnumerable<object> attributes, ModelMetadata modelMetadata)
+        public static BindingInfo? GetBindingInfo(IEnumerable<object> attributes, ModelMetadata modelMetadata)
         {
             if (attributes == null)
             {

src/Mvc/Mvc.Abstractions/src/ModelBinding/BindingSource.cs

@@ -12,7 +12,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
     /// A metadata object representing a source of data for model binding.
     /// </summary>
     [DebuggerDisplay("Source: {DisplayName}")]
-    public class BindingSource : IEquatable<BindingSource>
+    public class BindingSource : IEquatable<BindingSource?>
     {
         /// <summary>
         /// A <see cref="BindingSource"/> for the request body.
@@ -210,13 +210,13 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         }
 
         /// <inheritdoc />
-        public bool Equals(BindingSource other)
+        public bool Equals(BindingSource? other)
         {
             return string.Equals(other?.Id, Id, StringComparison.Ordinal);
         }
 
         /// <inheritdoc />
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             return Equals(obj as BindingSource);
         }
@@ -228,7 +228,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         }
 
         /// <inheritdoc />
-        public static bool operator ==(BindingSource s1, BindingSource s2)
+        public static bool operator ==(BindingSource? s1, BindingSource? s2)
         {
             if (s1 is null)
             {
@@ -239,7 +239,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         }
 
         /// <inheritdoc />
-        public static bool operator !=(BindingSource s1, BindingSource s2)
+        public static bool operator !=(BindingSource? s1, BindingSource? s2)
         {
             return !(s1 == s2);
         }

src/Mvc/Mvc.Abstractions/src/ModelBinding/CompositeBindingSource.cs

@@ -89,7 +89,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// <inheritdoc />
         public override bool CanAcceptDataFrom(BindingSource bindingSource)
         {
-            if (bindingSource == null)
+            if (bindingSource is null)
             {
                 throw new ArgumentNullException(nameof(bindingSource));
             }

src/Mvc/Mvc.Abstractions/src/ModelBinding/IBindingSourceMetadata.cs

@@ -15,6 +15,6 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// The <see cref="BindingSource"/> is metadata which can be used to determine which data
         /// sources are valid for model binding of a property or parameter.
         /// </remarks>
-        BindingSource BindingSource { get; }
+        BindingSource? BindingSource { get; }
     }
 }

src/Mvc/Mvc.Abstractions/src/ModelBinding/Metadata/ModelBindingMessageProvider.cs

@@ -17,28 +17,28 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Metadata
         /// <value>
         /// Default <see cref="string"/> is "A value for the '{0}' parameter or property was not provided.".
         /// </value>
-        public virtual Func<string, string> MissingBindRequiredValueAccessor { get; }
+        public virtual Func<string, string> MissingBindRequiredValueAccessor { get; } = default!;
 
         /// <summary>
         /// Error message the model binding system adds when either the key or the value of a
         /// <see cref="System.Collections.Generic.KeyValuePair{TKey, TValue}"/> is bound but not both.
         /// </summary>
         /// <value>Default <see cref="string"/> is "A value is required.".</value>
-        public virtual Func<string> MissingKeyOrValueAccessor { get; }
+        public virtual Func<string> MissingKeyOrValueAccessor { get; } = default!;
 
         /// <summary>
         /// Error message the model binding system adds when no value is provided for the request body,
         /// but a value is required.
         /// </summary>
         /// <value>Default <see cref="string"/> is "A non-empty request body is required.".</value>
-        public virtual Func<string> MissingRequestBodyRequiredValueAccessor { get; }
+        public virtual Func<string> MissingRequestBodyRequiredValueAccessor { get; } = default!;
 
         /// <summary>
         /// Error message the model binding system adds when a <c>null</c> value is bound to a
         /// non-<see cref="Nullable"/> property.
         /// </summary>
         /// <value>Default <see cref="string"/> is "The value '{0}' is invalid.".</value>
-        public virtual Func<string, string> ValueMustNotBeNullAccessor { get; }
+        public virtual Func<string, string> ValueMustNotBeNullAccessor { get; } = default!;
 
         /// <summary>
         /// Error message the model binding system adds when <see cref="ModelError.Exception"/> is of type
@@ -46,7 +46,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Metadata
         /// with a property.
         /// </summary>
         /// <value>Default <see cref="string"/> is "The value '{0}' is not valid for {1}.".</value>
-        public virtual Func<string, string, string> AttemptedValueIsInvalidAccessor { get; }
+        public virtual Func<string, string, string> AttemptedValueIsInvalidAccessor { get; } = default!;
 
         /// <summary>
         /// Error message the model binding system adds when <see cref="ModelError.Exception"/> is of type
@@ -54,7 +54,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Metadata
         /// with a collection element or action parameter.
         /// </summary>
         /// <value>Default <see cref="string"/> is "The value '{0}' is not valid.".</value>
-        public virtual Func<string, string> NonPropertyAttemptedValueIsInvalidAccessor { get; }
+        public virtual Func<string, string> NonPropertyAttemptedValueIsInvalidAccessor { get; } = default!;
 
         /// <summary>
         /// Error message the model binding system adds when <see cref="ModelError.Exception"/> is of type
@@ -62,7 +62,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Metadata
         /// with a property.
         /// </summary>
         /// <value>Default <see cref="string"/> is "The supplied value is invalid for {0}.".</value>
-        public virtual Func<string, string> UnknownValueIsInvalidAccessor { get; }
+        public virtual Func<string, string> UnknownValueIsInvalidAccessor { get; } = default!;
 
         /// <summary>
         /// Error message the model binding system adds when <see cref="ModelError.Exception"/> is of type
@@ -70,21 +70,21 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Metadata
         /// with a collection element or action parameter.
         /// </summary>
         /// <value>Default <see cref="string"/> is "The supplied value is invalid.".</value>
-        public virtual Func<string> NonPropertyUnknownValueIsInvalidAccessor { get; }
+        public virtual Func<string> NonPropertyUnknownValueIsInvalidAccessor { get; } = default!;
 
         /// <summary>
         /// Fallback error message HTML and tag helpers display when a property is invalid but the
         /// <see cref="ModelError"/>s have <c>null</c> <see cref="ModelError.ErrorMessage"/>s.
         /// </summary>
         /// <value>Default <see cref="string"/> is "The value '{0}' is invalid.".</value>
-        public virtual Func<string, string> ValueIsInvalidAccessor { get; }
+        public virtual Func<string, string> ValueIsInvalidAccessor { get; } = default!;
 
         /// <summary>
         /// Error message HTML and tag helpers add for client-side validation of numeric formats. Visible in the
         /// browser if the field for a <c>float</c> (for example) property does not have a correctly-formatted value.
         /// </summary>
         /// <value>Default <see cref="string"/> is "The field {0} must be a number.".</value>
-        public virtual Func<string, string> ValueMustBeANumberAccessor { get; }
+        public virtual Func<string, string> ValueMustBeANumberAccessor { get; } = default!;
 
         /// <summary>
         /// Error message HTML and tag helpers add for client-side validation of numeric formats. Visible in the
@@ -92,6 +92,6 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Metadata
         /// correctly-formatted value.
         /// </summary>
         /// <value>Default <see cref="string"/> is "The field must be a number.".</value>
-        public virtual Func<string> NonPropertyValueMustBeANumberAccessor { get; }
+        public virtual Func<string> NonPropertyValueMustBeANumberAccessor { get; } = default!;
     }
 }

src/Mvc/Mvc.Abstractions/src/ModelBinding/Metadata/ModelMetadataIdentity.cs

@@ -4,7 +4,6 @@
 using System;
 using System.Reflection;
 using Microsoft.AspNetCore.Mvc.Abstractions;
-using Microsoft.Extensions.Internal;
 
 namespace Microsoft.AspNetCore.Mvc.ModelBinding.Metadata
 {
@@ -15,9 +14,9 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Metadata
     {
         private ModelMetadataIdentity(
             Type modelType,
-            string name = null,
+            string? name = null,
-            Type containerType = null,
+            Type? containerType = null,
-            object fieldInfo = null)
+            object? fieldInfo = null)
         {
             ModelType = modelType;
             Name = name;
@@ -107,7 +106,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Metadata
         /// <param name="parameter">The <see cref="ParameterInfo" />.</param>
         /// <returns>A <see cref="ModelMetadataIdentity"/>.</returns>
         public static ModelMetadataIdentity ForParameter(ParameterInfo parameter)
-            => ForParameter(parameter, parameter?.ParameterType);
+            => ForParameter(parameter, parameter.ParameterType);
 
         /// <summary>
         /// Creates a <see cref="ModelMetadataIdentity"/> for the provided parameter with the specified
@@ -135,7 +134,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Metadata
         /// Gets the <see cref="Type"/> defining the model property represented by the current
         /// instance, or <c>null</c> if the current instance does not represent a property.
         /// </summary>
-        public Type ContainerType { get; }
+        public Type? ContainerType { get; }
 
         /// <summary>
         /// Gets the <see cref="Type"/> represented by the current instance.
@@ -168,21 +167,21 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Metadata
         /// Gets the name of the current instance if it represents a parameter or property, or <c>null</c> if
         /// the current instance represents a type.
         /// </summary>
-        public string Name { get; }
+        public string? Name { get; }
 
-        private object FieldInfo { get; }
+        private object? FieldInfo { get; }
 
         /// <summary>
         /// Gets a descriptor for the parameter, or <c>null</c> if this instance
         /// does not represent a parameter.
         /// </summary>
-        public ParameterInfo ParameterInfo => FieldInfo as ParameterInfo;
+        public ParameterInfo? ParameterInfo => FieldInfo as ParameterInfo;
 
         /// <summary>
         /// Gets a descriptor for the property, or <c>null</c> if this instance
         /// does not represent a property.
         /// </summary>
-        public PropertyInfo PropertyInfo => FieldInfo as PropertyInfo;
+        public PropertyInfo? PropertyInfo => FieldInfo as PropertyInfo;
 
         /// <inheritdoc />
         public bool Equals(ModelMetadataIdentity other)
@@ -196,7 +195,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Metadata
         }
 
         /// <inheritdoc />
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             var other = obj as ModelMetadataIdentity?;
             return other.HasValue && Equals(other.Value);
@@ -205,13 +204,13 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Metadata
         /// <inheritdoc />
         public override int GetHashCode()
         {
-            var hash = new HashCodeCombiner();
+            var hash = new HashCode();
             hash.Add(ContainerType);
             hash.Add(ModelType);
             hash.Add(Name, StringComparer.Ordinal);
             hash.Add(ParameterInfo);
             hash.Add(PropertyInfo);
-            return hash;
+            return hash.ToHashCode();
         }
     }
 }

src/Mvc/Mvc.Abstractions/src/ModelBinding/ModelBinderProviderContext.cs

@@ -48,6 +48,6 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// <summary>
         /// Gets the <see cref="IServiceProvider"/>.
         /// </summary>
-        public virtual IServiceProvider Services { get; }
+        public virtual IServiceProvider Services { get; } = default!;
     }
 }

src/Mvc/Mvc.Abstractions/src/ModelBinding/ModelBindingContext.cs

@@ -39,7 +39,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// <summary>
         /// Gets the <see cref="Http.HttpContext"/> associated with this context.
         /// </summary>
-        public virtual HttpContext HttpContext => ActionContext?.HttpContext;
+        public virtual HttpContext HttpContext => ActionContext?.HttpContext!;
 
         /// <summary>
         /// Gets or sets an indication that the current binder is handling the top-level object.
@@ -71,7 +71,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// Gets or sets the name of the top-level model. This is not reset to <see cref="string.Empty"/> when value
         /// providers have no match for that model.
         /// </summary>
-        public string OriginalModelName { get; protected set; }
+        public string OriginalModelName { get; protected set; } = default!;
 
         /// <summary>
         /// Gets or sets the <see cref="ModelStateDictionary"/> used to capture <see cref="ModelStateEntry"/> values

src/Mvc/Mvc.Abstractions/src/ModelBinding/ModelBindingResult.cs

@@ -2,7 +2,6 @@
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
 using System;
-using Microsoft.Extensions.Internal;
 
 namespace Microsoft.AspNetCore.Mvc.ModelBinding
 {
@@ -19,7 +18,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         {
             return new ModelBindingResult(model: null, isModelSet: false);
         }
-        
+
         /// <summary>
         /// Creates a <see cref="ModelBindingResult"/> representing a successful model binding operation.
         /// </summary>
@@ -27,10 +26,10 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// <returns>A <see cref="ModelBindingResult"/> representing a successful model bind.</returns>
         public static ModelBindingResult Success(object model)
         {
-            return new ModelBindingResult( model, isModelSet: true);
+            return new ModelBindingResult(model, isModelSet: true);
         }
 
-        private ModelBindingResult(object model, bool isModelSet)
+        private ModelBindingResult(object? model, bool isModelSet)
         {
             Model = model;
             IsModelSet = isModelSet;
@@ -39,7 +38,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// <summary>
         /// Gets the model associated with this context.
         /// </summary>
-        public object Model { get; }
+        public object? Model { get; }
 
         /// <summary>
         /// <para>
@@ -53,7 +52,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         public bool IsModelSet { get; }
 
         /// <inheritdoc />
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             var other = obj as ModelBindingResult?;
             if (other == null)
@@ -69,11 +68,11 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// <inheritdoc />
         public override int GetHashCode()
         {
-            var hashCodeCombiner = HashCodeCombiner.Start();
+            var hashCodeCombiner = new HashCode();
             hashCodeCombiner.Add(IsModelSet);
             hashCodeCombiner.Add(Model);
 
-            return hashCodeCombiner.CombinedHash;
+            return hashCodeCombiner.ToHashCode();
         }
 
         /// <inheritdoc />

src/Mvc/Mvc.Abstractions/src/ModelBinding/ModelError.cs

@@ -25,7 +25,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// </summary>
         /// <param name="exception">The <see cref="System.Exception"/>.</param>
         /// <param name="errorMessage">The error message.</param>
-        public ModelError(Exception exception, string errorMessage)
+        public ModelError(Exception exception, string? errorMessage)
             : this(errorMessage)
         {
             Exception = exception ?? throw new ArgumentNullException(nameof(exception));
@@ -35,7 +35,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// Initializes a new instance of <see cref="ModelError"/> with the specified <paramref name="errorMessage"/>.
         /// </summary>
         /// <param name="errorMessage">The error message.</param>
-        public ModelError(string errorMessage)
+        public ModelError(string? errorMessage)
         {
             ErrorMessage = errorMessage ?? string.Empty;
         }
@@ -43,7 +43,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// <summary>
         /// Gets the <see cref="System.Exception"/> associated with this <see cref="ModelError"/> instance.
         /// </summary>
-        public Exception Exception { get; }
+        public Exception? Exception { get; }
 
         /// <summary>
         /// Gets the error message associated with this <see cref="ModelError"/> instance.

src/Mvc/Mvc.Abstractions/src/ModelBinding/ModelMetadata.cs

@@ -17,7 +17,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
     /// A metadata representation of a model type, property or parameter.
     /// </summary>
     [DebuggerDisplay("{DebuggerToString(),nq}")]
-    public abstract class ModelMetadata : IEquatable<ModelMetadata>, IModelMetadataProvider
+    public abstract class ModelMetadata : IEquatable<ModelMetadata?>, IModelMetadataProvider
     {
         /// <summary>
         /// The default value of <see cref="ModelMetadata.Order"/>.
@@ -40,7 +40,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// <summary>
         /// Gets the type containing the property if this metadata is for a property; <see langword="null"/> otherwise.
         /// </summary>
-        public Type ContainerType => Identity.ContainerType;
+        public Type? ContainerType => Identity.ContainerType;
 
         /// <summary>
         /// Gets the metadata for <see cref="ContainerType"/> if this metadata is for a property;
@@ -68,17 +68,17 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// Gets the name of the parameter or property if this metadata is for a parameter or property;
         /// <see langword="null"/> otherwise i.e. if this is the metadata for a type.
         /// </summary>
-        public string Name => Identity.Name;
+        public string? Name => Identity.Name;
 
         /// <summary>
         /// Gets the name of the parameter if this metadata is for a parameter; <see langword="null"/> otherwise.
         /// </summary>
-        public string ParameterName => MetadataKind == ModelMetadataKind.Parameter ? Identity.Name : null;
+        public string? ParameterName => MetadataKind == ModelMetadataKind.Parameter ? Identity.Name : null;
 
         /// <summary>
         /// Gets the name of the property if this metadata is for a property; <see langword="null"/> otherwise.
         /// </summary>
-        public string PropertyName => MetadataKind == ModelMetadataKind.Property ? Identity.Name : null;
+        public string? PropertyName => MetadataKind == ModelMetadataKind.Property ? Identity.Name : null;
 
         /// <summary>
         /// Gets the key for the current instance.
@@ -155,7 +155,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// implements <see cref="IEnumerable"/> but not <see cref="IEnumerable{T}"/>. <c>null</c> otherwise i.e. when
         /// <see cref="IsEnumerableType"/> is <c>false</c>.
         /// </value>
-        public abstract ModelMetadata ElementMetadata { get; }
+        public abstract ModelMetadata? ElementMetadata { get; }
 
         /// <summary>
         /// Gets the ordered and grouped display names and values of all <see cref="Enum"/> values in
@@ -318,7 +318,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// validated. If <c>null</c>, properties with this <see cref="ModelMetadata"/> are validated.
         /// </summary>
         /// <value>Defaults to <c>null</c>.</value>
-        public virtual IPropertyValidationFilter PropertyValidationFilter => null;
+        public virtual IPropertyValidationFilter? PropertyValidationFilter => null;
 
         /// <summary>
         /// Gets a value that indicates whether properties or elements of the model should be validated.
@@ -343,7 +343,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// Gets the <see cref="Type"/> for elements of <see cref="ModelType"/> if that <see cref="Type"/>
         /// implements <see cref="IEnumerable"/>.
         /// </summary>
-        public Type ElementType { get; private set; }
+        public Type? ElementType { get; private set; }
 
         /// <summary>
         /// Gets a value indicating whether <see cref="ModelType"/> is a complex type.
@@ -389,7 +389,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// <remarks>
         /// Identical to <see cref="ModelType"/> unless <see cref="IsNullableValueType"/> is <c>true</c>.
         /// </remarks>
-        public Type UnderlyingOrModelType { get; private set; }
+        public Type UnderlyingOrModelType { get; private set; } = default!;
 
         /// <summary>
         /// Gets a property getter delegate to get the property value from a model object.
@@ -415,7 +415,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         }
 
         /// <inheritdoc />
-        public bool Equals(ModelMetadata other)
+        public bool Equals(ModelMetadata? other)
         {
             if (object.ReferenceEquals(this, other))
             {
@@ -433,7 +433,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         }
 
         /// <inheritdoc />
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             return Equals(obj as ModelMetadata);
         }
@@ -469,14 +469,14 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
             else if (ModelType.IsArray)
             {
                 IsEnumerableType = true;
-                ElementType = ModelType.GetElementType();
+                ElementType = ModelType.GetElementType()!;
             }
             else
             {
                 IsEnumerableType = true;
 
                 var enumerableType = ClosedGenericMatcher.ExtractGenericInterface(ModelType, typeof(IEnumerable<>));
-                ElementType = enumerableType?.GenericTypeArguments[0];
+                ElementType = enumerableType?.GenericTypeArguments[0]!;
 
                 if (ElementType == null)
                 {
@@ -497,7 +497,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
                 case ModelMetadataKind.Parameter:
                     return $"ModelMetadata (Parameter: '{ParameterName}' Type: '{ModelType.Name}')";
                 case ModelMetadataKind.Property:
-                    return $"ModelMetadata (Property: '{ContainerType.Name}.{PropertyName}' Type: '{ModelType.Name}')";
+                    return $"ModelMetadata (Property: '{ContainerType!.Name}.{PropertyName}' Type: '{ModelType.Name}')";
                 case ModelMetadataKind.Type:
                     return $"ModelMetadata (Type: '{ModelType.Name}')";
                 default:

src/Mvc/Mvc.Abstractions/src/ModelBinding/ModelPropertyCollection.cs

@@ -32,7 +32,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// The <see cref="ModelMetadata"/> instance for the property specified by <paramref name="propertyName"/>, or
         /// <c>null</c> if no match can be found.
         /// </returns>
-        public ModelMetadata this[string propertyName]
+        public ModelMetadata? this[string propertyName]
         {
             get
             {

src/Mvc/Mvc.Abstractions/src/ModelBinding/ModelStateDictionary.cs

@@ -5,6 +5,7 @@ using System;
 using System.Collections;
 using System.Collections.Generic;
 using System.Diagnostics;
+using System.Diagnostics.CodeAnalysis;
 using System.Runtime.CompilerServices;
 using Microsoft.AspNetCore.Mvc.Abstractions;
 using Microsoft.AspNetCore.Mvc.Formatters;
@@ -166,7 +167,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
                 }
 
                 TryGetValue(key, out var entry);
-                return entry;
+                return entry!;
             }
         }
 
@@ -305,15 +306,15 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
                 }
                 else if (entry == null)
                 {
-                    errorMessage = messageProvider.UnknownValueIsInvalidAccessor(name);
+                    errorMessage = messageProvider.UnknownValueIsInvalidAccessor(name!);
                 }
                 else if (name == null)
                 {
-                    errorMessage = messageProvider.NonPropertyAttemptedValueIsInvalidAccessor(entry.AttemptedValue);
+                    errorMessage = messageProvider.NonPropertyAttemptedValueIsInvalidAccessor(entry.AttemptedValue!);
                 }
                 else
                 {
-                    errorMessage = messageProvider.AttemptedValueIsInvalidAccessor(entry.AttemptedValue, name);
+                    errorMessage = messageProvider.AttemptedValueIsInvalidAccessor(entry.AttemptedValue!, name);
                 }
 
                 return TryAddModelError(key, errorMessage);
@@ -511,7 +512,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// <param name="attemptedValue">
         /// The values of <paramref name="rawValue"/> in a comma-separated <see cref="string"/>.
         /// </param>
-        public void SetModelValue(string key, object rawValue, string attemptedValue)
+        public void SetModelValue(string key, object? rawValue, string attemptedValue)
         {
             if (key == null)
             {
@@ -540,7 +541,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
             }
 
             // Avoid creating a new array for rawValue if there's only one value.
-            object rawValue;
+            object? rawValue;
             if (valueProviderResult == ValueProviderResult.None)
             {
                 rawValue = null;
@@ -573,10 +574,8 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
             }
         }
 
-        private ModelStateNode GetNode(string key)
+        private ModelStateNode? GetNode(string key)
         {
-            Debug.Assert(key != null);
-
             var current = _root;
             if (key.Length > 0)
             {
@@ -661,7 +660,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
             return new StringSegment(key, keyStart, index - keyStart);
         }
 
-        private static ModelValidationState? GetValidity(ModelStateNode node)
+        private static ModelValidationState? GetValidity(ModelStateNode? node)
         {
             if (node == null)
             {
@@ -774,7 +773,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         }
 
         /// <inheritdoc />
-        public bool TryGetValue(string key, out ModelStateEntry value)
+        public bool TryGetValue(string key, [NotNullWhen(true)] out ModelStateEntry? value)
         {
             if (key == null)
             {
@@ -893,11 +892,11 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
                 SubKey = subKey;
             }
 
-            public List<ModelStateNode> ChildNodes { get; set; }
+            public List<ModelStateNode>? ChildNodes { get; set; }
 
-            public override IReadOnlyList<ModelStateEntry> Children => ChildNodes;
+            public override IReadOnlyList<ModelStateEntry>? Children => ChildNodes;
 
-            public string Key { get; set; }
+            public string Key { get; set; } = default!;
 
             public StringSegment SubKey { get; }
 
@@ -931,9 +930,9 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
             }
 
             [MethodImpl(MethodImplOptions.AggressiveInlining)]
-            public ModelStateNode GetNode(StringSegment subKey)
+            public ModelStateNode? GetNode(StringSegment subKey)
             {
-                ModelStateNode modelStateNode = null;
+                ModelStateNode? modelStateNode = null;
                 if (subKey.Length == 0)
                 {
                     modelStateNode = this;
@@ -981,7 +980,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
                 return modelStateNode;
             }
 
-            public override ModelStateEntry GetModelStateForProperty(string propertyName)
+            public override ModelStateEntry? GetModelStateForProperty(string propertyName)
                 => GetNode(new StringSegment(propertyName));
 
             private int BinarySearch(StringSegment searchKey)
@@ -1068,9 +1067,9 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// </summary>
         public struct Enumerator : IEnumerator<KeyValuePair<string, ModelStateEntry>>
         {
-            private readonly ModelStateNode _rootNode;
+            private readonly ModelStateNode? _rootNode;
             private ModelStateNode _modelStateNode;
-            private List<ModelStateNode> _nodes;
+            private List<ModelStateNode>? _nodes;
             private int _index;
             private bool _visitedRoot;
 
@@ -1093,7 +1092,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
 
                 _index = -1;
                 _rootNode = dictionary.GetNode(prefix);
-                _modelStateNode = null;
+                _modelStateNode = default!;
                 _nodes = null;
                 _visitedRoot = false;
             }
@@ -1141,7 +1140,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
                 while (_nodes.Count > 0)
                 {
                     var node = _nodes[0];
-                    if (_index == node.ChildNodes.Count - 1)
+                    if (_index == node.ChildNodes!.Count - 1)
                     {
                         // We've exhausted the current sublist.
                         _nodes.RemoveAt(0);
@@ -1173,9 +1172,9 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
             public void Reset()
             {
                 _index = -1;
-                _nodes.Clear();
+                _nodes?.Clear();
                 _visitedRoot = false;
-                _modelStateNode = null;
+                _modelStateNode = default!;
             }
         }
 
@@ -1218,7 +1217,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
             public KeyEnumerator(ModelStateDictionary dictionary, string prefix)
             {
                 _prefixEnumerator = new Enumerator(dictionary, prefix);
-                Current = null;
+                Current = default!;
             }
 
             /// <inheritdoc />
@@ -1240,7 +1239,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
                 }
                 else
                 {
-                    Current = null;
+                    Current = default!;
                 }
 
                 return result;
@@ -1250,7 +1249,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
             public void Reset()
             {
                 _prefixEnumerator.Reset();
-                Current = null;
+                Current = default!;
             }
         }
 
@@ -1293,7 +1292,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
             public ValueEnumerator(ModelStateDictionary dictionary, string prefix)
             {
                 _prefixEnumerator = new Enumerator(dictionary, prefix);
-                Current = null;
+                Current = default!;
             }
 
             /// <inheritdoc />
@@ -1315,7 +1314,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
                 }
                 else
                 {
-                    Current = null;
+                    Current = default!;
                 }
 
                 return result;
@@ -1325,7 +1324,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
             public void Reset()
             {
                 _prefixEnumerator.Reset();
-                Current = null;
+                Current = default!;
             }
         }
     }

src/Mvc/Mvc.Abstractions/src/ModelBinding/ModelStateEntry.cs

@@ -10,17 +10,17 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
     /// </summary>
     public abstract class ModelStateEntry
     {
-        private ModelErrorCollection _errors;
+        private ModelErrorCollection? _errors;
 
         /// <summary>
         /// Gets the raw value from the request associated with this entry.
         /// </summary>
-        public object RawValue { get; set; }
+        public object? RawValue { get; set; }
 
         /// <summary>
         /// Gets the set of values contained in <see cref="RawValue"/>, joined into a comma-separated string.
         /// </summary>
-        public string AttemptedValue { get; set; }
+        public string? AttemptedValue { get; set; }
 
         /// <summary>
         /// Gets the <see cref="ModelErrorCollection"/> for this entry.
@@ -61,7 +61,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// This method returns any existing entry, even those with <see cref="IsContainerNode"/> with value
         /// <see langword="true"/>.
         /// </remarks>
-        public abstract ModelStateEntry GetModelStateForProperty(string propertyName);
+        public abstract ModelStateEntry? GetModelStateForProperty(string propertyName);
 
         /// <summary>
         /// Gets the <see cref="ModelStateEntry"/> values for sub-properties.
@@ -70,6 +70,6 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// This property returns all existing entries, even those with <see cref="IsContainerNode"/> with value
         /// <see langword="true"/>.
         /// </remarks>
-        public abstract IReadOnlyList<ModelStateEntry> Children { get; }
+        public abstract IReadOnlyList<ModelStateEntry>? Children { get; }
     }
 }

src/Mvc/Mvc.Abstractions/src/ModelBinding/Validation/ClientValidatorItem.cs

@@ -30,12 +30,12 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Validation
         /// <summary>
         /// Gets the metadata associated with the <see cref="Validator"/>.
         /// </summary>
-        public object ValidatorMetadata { get; }
+        public object ValidatorMetadata { get; } = default!;
 
         /// <summary>
         /// Gets or sets the <see cref="IClientModelValidator"/>.
         /// </summary>
-        public IClientModelValidator Validator { get; set; }
+        public IClientModelValidator Validator { get; set; } = default!;
 
         /// <summary>
         /// Gets or sets a value indicating whether or not <see cref="Validator"/> can be reused across requests.

src/Mvc/Mvc.Abstractions/src/ModelBinding/Validation/ValidationEntry.cs

@@ -10,8 +10,8 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Validation
     /// </summary>
     public struct ValidationEntry
     {
-        private object _model;
+        private object? _model;
-        private Func<object> _modelAccessor;
+        private Func<object>? _modelAccessor;
 
         /// <summary>
         /// Creates a new <see cref="ValidationEntry"/>.
@@ -79,7 +79,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Validation
         /// <summary>
         /// The model object.
         /// </summary>
-        public object Model
+        public object? Model
         {
             get
             {

src/Mvc/Mvc.Abstractions/src/ModelBinding/Validation/ValidationStateDictionary.cs

@@ -4,7 +4,7 @@
 using System;
 using System.Collections;
 using System.Collections.Generic;
-using System.Runtime.CompilerServices;
+using System.Diagnostics.CodeAnalysis;
 
 namespace Microsoft.AspNetCore.Mvc.ModelBinding.Validation
 {
@@ -25,8 +25,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Validation
             _inner = new Dictionary<object, ValidationStateEntry>(ReferenceEqualityComparer.Instance);
         }
 
-        /// <inheritdoc />
+        public ValidationStateEntry? this[object key]
-        public ValidationStateEntry this[object key]
         {
             get
             {
@@ -36,10 +35,19 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Validation
 
             set
             {
-                _inner[key] = value;
+                _inner[key] = value!;
             }
         }
 
+        /// <inheritdoc />
+        ValidationStateEntry IDictionary<object, ValidationStateEntry>.this[object key]
+        {
+            get => this[key]!;
+            set => this[key] = value;
+        }
+
+        ValidationStateEntry IReadOnlyDictionary<object, ValidationStateEntry>.this[object key] => this[key]!;
+
         /// <inheritdoc />
         public int Count => _inner.Count;
 
@@ -115,7 +123,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Validation
         }
 
         /// <inheritdoc />
-        public bool TryGetValue(object key, out ValidationStateEntry value)
+        public bool TryGetValue(object key, [MaybeNullWhen(false)] out ValidationStateEntry value)
         {
             return _inner.TryGetValue(key, out value);
         }
@@ -125,30 +133,5 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Validation
         {
             return ((IDictionary<object, ValidationStateEntry>)_inner).GetEnumerator();
         }
-
-        private class ReferenceEqualityComparer : IEqualityComparer<object>
-        {
-            private static readonly bool IsMono = Type.GetType("Mono.Runtime") != null;
-
-            public static readonly ReferenceEqualityComparer Instance = new ReferenceEqualityComparer();
-
-            public new bool Equals(object x, object y)
-            {
-                return Object.ReferenceEquals(x, y);
-            }
-
-            public int GetHashCode(object obj)
-            {
-                // RuntimeHelpers.GetHashCode sometimes crashes the runtime on Mono 4.0.4
-                // See: https://github.com/aspnet/External/issues/45
-                // The workaround here is to just not hash anything, and fall back to an equality check.
-                if (IsMono)
-                {
-                    return 0;
-                }
-
-                return RuntimeHelpers.GetHashCode(obj);
-            }
-        }
     }
 }

src/Mvc/Mvc.Abstractions/src/ModelBinding/Validation/ValidationStateEntry.cs

@@ -12,12 +12,12 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Validation
         /// <summary>
         /// Gets or sets the model prefix associated with the entry.
         /// </summary>
-        public string Key { get; set; }
+        public string Key { get; set; } = default!;
 
         /// <summary>
         /// Gets or sets the <see cref="ModelMetadata"/> associated with the entry.
         /// </summary>
-        public ModelMetadata Metadata { get; set; }
+        public ModelMetadata Metadata { get; set; } = default!;
 
         /// <summary>
         /// Gets or sets a value indicating whether the associated model object should be validated.
@@ -28,6 +28,6 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Validation
         /// Gets or sets an <see cref="IValidationStrategy"/> for enumerating child entries of the associated
         /// model object.
         /// </summary>
-        public IValidationStrategy Strategy { get; set; }
+        public IValidationStrategy Strategy { get; set; } = default!;
     }
 }

src/Mvc/Mvc.Abstractions/src/ModelBinding/Validation/ValidatorItem.cs

@@ -30,12 +30,12 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding.Validation
         /// <summary>
         /// Gets the metadata associated with the <see cref="Validator"/>.
         /// </summary>
-        public object ValidatorMetadata { get; }
+        public object ValidatorMetadata { get; } = default!;
 
         /// <summary>
         /// Gets or sets the <see cref="IModelValidator"/>.
         /// </summary>
-        public IModelValidator Validator { get; set; }
+        public IModelValidator Validator { get; set; } = default!;
 
         /// <summary>
         /// Gets or sets a value indicating whether or not <see cref="Validator"/> can be reused across requests.

src/Mvc/Mvc.Abstractions/src/ModelBinding/ValueProviderResult.cs

@@ -69,7 +69,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         /// to get a single value for processing regardless of whether a single or multiple values were provided
         /// in the request.
         /// </summary>
-        public string FirstValue
+        public string? FirstValue
         {
             get
             {
@@ -87,7 +87,7 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
         public int Length => Values.Count;
 
         /// <inheritdoc />
-        public override bool Equals(object obj)
+        public override bool Equals(object? obj)
         {
             var other = obj as ValueProviderResult?;
             return other.HasValue && Equals(other.Value);

src/Mvc/Mvc.Abstractions/src/Routing/AttributeRouteInfo.cs

@@ -13,7 +13,7 @@ namespace Microsoft.AspNetCore.Mvc.Routing
         /// <summary>
         /// The route template. May be null if the action has no attribute routes.
         /// </summary>
-        public string Template { get; set; }
+        public string? Template { get; set; }
 
         /// <summary>
         /// Gets the order of the route associated with a given action. This property determines
@@ -27,7 +27,7 @@ namespace Microsoft.AspNetCore.Mvc.Routing
         /// to generate a link by referring to the route by name instead of attempting to match a
         /// route by provided route data.
         /// </summary>
-        public string Name { get; set; }
+        public string Name { get; set; } = default!;
 
         /// <summary>
         /// Gets or sets a value that determines if the route entry associated with this model participates in link generation.

src/Mvc/Mvc.Abstractions/src/Routing/UrlActionContext.cs

@@ -11,7 +11,7 @@ namespace Microsoft.AspNetCore.Mvc.Routing
         /// <summary>
         /// The name of the action method that <see cref="IUrlHelper.Action(UrlActionContext)"/> uses to generate URLs.
         /// </summary>
-        public string Action
+        public string? Action
         {
             get;
             set;
@@ -20,7 +20,7 @@ namespace Microsoft.AspNetCore.Mvc.Routing
         /// <summary>
         /// The name of the controller that <see cref="IUrlHelper.Action(UrlActionContext)"/> uses to generate URLs.
         /// </summary>
-        public string Controller
+        public string? Controller
         {
             get;
             set;
@@ -30,7 +30,7 @@ namespace Microsoft.AspNetCore.Mvc.Routing
         /// The object that contains the route values that <see cref="IUrlHelper.Action(UrlActionContext)"/>
         /// uses to generate URLs.
         /// </summary>
-        public object Values
+        public object? Values
         {
             get;
             set;
@@ -40,7 +40,7 @@ namespace Microsoft.AspNetCore.Mvc.Routing
         /// The protocol for the URLs that <see cref="IUrlHelper.Action(UrlActionContext)"/> generates,
         /// such as "http" or "https"
         /// </summary>
-        public string Protocol
+        public string? Protocol
         {
             get;
             set;
@@ -49,7 +49,7 @@ namespace Microsoft.AspNetCore.Mvc.Routing
         /// <summary>
         /// The host name for the URLs that <see cref="IUrlHelper.Action(UrlActionContext)"/> generates.
         /// </summary>
-        public string Host
+        public string? Host
         {
             get;
             set;
@@ -58,7 +58,7 @@ namespace Microsoft.AspNetCore.Mvc.Routing
         /// <summary>
         /// The fragment for the URLs that <see cref="IUrlHelper.Action(UrlActionContext)"/> generates.
         /// </summary>
-        public string Fragment
+        public string? Fragment
         {
             get;
             set;

src/Mvc/Mvc.Abstractions/src/Routing/UrlRouteContext.cs

@@ -11,7 +11,7 @@ namespace Microsoft.AspNetCore.Mvc.Routing
         /// <summary>
         /// The name of the route that <see cref="IUrlHelper.RouteUrl(UrlRouteContext)"/> uses to generate URLs.
         /// </summary>
-        public string RouteName
+        public string? RouteName
         {
             get;
             set;
@@ -21,7 +21,7 @@ namespace Microsoft.AspNetCore.Mvc.Routing
         /// The object that contains the route values that <see cref="IUrlHelper.RouteUrl(UrlRouteContext)"/>
         /// uses to generate URLs.
         /// </summary>
-        public object Values
+        public object? Values
         {
             get;
             set;
@@ -31,7 +31,7 @@ namespace Microsoft.AspNetCore.Mvc.Routing
         /// The protocol for the URLs that <see cref="IUrlHelper.RouteUrl(UrlRouteContext)"/> generates,
         /// such as "http" or "https"
         /// </summary>
-        public string Protocol
+        public string? Protocol
         {
             get;
             set;
@@ -40,7 +40,7 @@ namespace Microsoft.AspNetCore.Mvc.Routing
         /// <summary>
         /// The host name for the URLs that <see cref="IUrlHelper.RouteUrl(UrlRouteContext)"/> generates.
         /// </summary>
-        public string Host
+        public string? Host
         {
             get;
             set;
@@ -49,7 +49,7 @@ namespace Microsoft.AspNetCore.Mvc.Routing
         /// <summary>
         /// The fragment for the URLs that <see cref="IUrlHelper.RouteUrl(UrlRouteContext)"/> generates.
         /// </summary>
-        public string Fragment
+        public string? Fragment
         {
             get;
             set;

src/Mvc/Mvc.ApiExplorer/src/DefaultApiDescriptionProvider.cs

@@ -662,11 +662,11 @@ namespace Microsoft.AspNetCore.Mvc.ApiExplorer
 
                 public int GetHashCode(PropertyKey obj)
                 {
-                    var hashCodeCombiner = HashCodeCombiner.Start();
+                    var hashCodeCombiner = new HashCode();
                     hashCodeCombiner.Add(obj.ContainerType);
                     hashCodeCombiner.Add(obj.PropertyName);
                     hashCodeCombiner.Add(obj.Source);
-                    return hashCodeCombiner.CombinedHash;
+                    return hashCodeCombiner.ToHashCode();
                 }
             }
         }

src/Mvc/Mvc.Core/src/ModelBinding/ModelBinderFactory.cs

@@ -319,10 +319,10 @@ namespace Microsoft.AspNetCore.Mvc.ModelBinding
 
             public override int GetHashCode()
             {
-                var hash = new HashCodeCombiner();
+                var hash = new HashCode();
                 hash.Add(_metadata);
                 hash.Add(RuntimeHelpers.GetHashCode(_token));
-                return hash;
+                return hash.ToHashCode();
             }
 
             public override string ToString()

src/Mvc/Mvc.Core/src/Routing/AttributeRoute.cs

@@ -291,10 +291,10 @@ namespace Microsoft.AspNetCore.Mvc.Routing
                     return 0;
                 }
 
-                var hash = new HashCodeCombiner();
+                var hash = new HashCode();
                 hash.Add(obj.Order);
                 hash.Add(obj.RouteTemplate.TemplateText, StringComparer.OrdinalIgnoreCase);
-                return hash;
+                return hash.ToHashCode();
             }
         }
 

src/Mvc/Mvc.Razor/src/RazorPageActivator.cs

@@ -123,14 +123,14 @@ namespace Microsoft.AspNetCore.Mvc.Razor
 
             public override int GetHashCode()
             {
-                var hashCodeCombiner = HashCodeCombiner.Start();
+                var hashCodeCombiner = new HashCode();
                 hashCodeCombiner.Add(PageType);
                 if (ProvidedModelType != null)
                 {
                     hashCodeCombiner.Add(ProvidedModelType);
                 }
 
-                return hashCodeCombiner.CombinedHash;
+                return hashCodeCombiner.ToHashCode();
             }
         }
     }

src/Mvc/Mvc.Razor/src/ViewLocationCacheKey.cs

@@ -135,7 +135,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor
         /// <inheritdoc />
         public override int GetHashCode()
         {
-            var hashCodeCombiner = HashCodeCombiner.Start();
+            var hashCodeCombiner = new HashCode();
             hashCodeCombiner.Add(IsMainPage ? 1 : 0);
             hashCodeCombiner.Add(ViewName, StringComparer.Ordinal);
             hashCodeCombiner.Add(ControllerName, StringComparer.Ordinal);
@@ -151,7 +151,7 @@ namespace Microsoft.AspNetCore.Mvc.Razor
                 }
             }
 
-            return hashCodeCombiner;
+            return hashCodeCombiner.ToHashCode();
         }
     }
 }

src/Mvc/Mvc.TagHelpers/src/Cache/CacheTagKey.cs

@@ -247,7 +247,7 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers.Cache
                 return _hashcode.Value;
             }
 
-            var hashCodeCombiner = new HashCodeCombiner();
+            var hashCodeCombiner = new HashCode();
 
             hashCodeCombiner.Add(Key, StringComparer.Ordinal);
             hashCodeCombiner.Add(_expiresAfter);
@@ -258,12 +258,12 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers.Cache
             hashCodeCombiner.Add(_requestCulture);
             hashCodeCombiner.Add(_requestUICulture);
 
-            CombineCollectionHashCode(hashCodeCombiner, VaryByCookieName, _cookies);
+            CombineCollectionHashCode(ref hashCodeCombiner, VaryByCookieName, _cookies);
-            CombineCollectionHashCode(hashCodeCombiner, VaryByHeaderName, _headers);
+            CombineCollectionHashCode(ref hashCodeCombiner, VaryByHeaderName, _headers);
-            CombineCollectionHashCode(hashCodeCombiner, VaryByQueryName, _queries);
+            CombineCollectionHashCode(ref hashCodeCombiner, VaryByQueryName, _queries);
-            CombineCollectionHashCode(hashCodeCombiner, VaryByRouteName, _routeValues);
+            CombineCollectionHashCode(ref hashCodeCombiner, VaryByRouteName, _routeValues);
 
-            _hashcode = hashCodeCombiner.CombinedHash;
+            _hashcode = hashCodeCombiner.ToHashCode();
 
             return _hashcode.Value;
         }
@@ -331,7 +331,7 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers.Cache
         }
 
         private static void CombineCollectionHashCode(
-            HashCodeCombiner hashCodeCombiner,
+            ref HashCode hashCodeCombiner,
             string collectionName,
             IList<KeyValuePair<string, string>> values)
         {

src/Mvc/Mvc.TagHelpers/src/GlobbingUrlBuilder.cs

@@ -3,6 +3,7 @@
 
 using System;
 using System.Collections.Generic;
+using System.Security.Policy;
 using Microsoft.AspNetCore.Http;
 using Microsoft.Extensions.Caching.Memory;
 using Microsoft.Extensions.FileProviders;
@@ -373,11 +374,11 @@ namespace Microsoft.AspNetCore.Mvc.TagHelpers
 
             public override int GetHashCode()
             {
-                var hashCodeCombiner = HashCodeCombiner.Start();
+                var hashCodeCombiner = new HashCode();
                 hashCodeCombiner.Add(Include);
                 hashCodeCombiner.Add(Exclude);
 
-                return hashCodeCombiner.CombinedHash;
+                return hashCodeCombiner.ToHashCode();
             }
         }
     }

src/Mvc/Mvc.ViewFeatures/src/LambdaExpressionComparer.cs

@@ -84,7 +84,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
         public int GetHashCode(LambdaExpression lambdaExpression)
         {
             var expression = lambdaExpression.Body;
-            var hashCodeCombiner = HashCodeCombiner.Start();
+            var hashCodeCombiner = new HashCode();
 
             while (true)
             {
@@ -107,7 +107,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
                 }
             }
 
-            return hashCodeCombiner.CombinedHash;
+            return hashCodeCombiner.ToHashCode();
         }
     }
 }

src/Mvc/Mvc.ViewFeatures/src/MemberExpressionCacheKeyComparer.cs

@@ -1,6 +1,7 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+using System;
 using System.Collections.Generic;
 using Microsoft.Extensions.Internal;
 
@@ -39,7 +40,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
 
         public int GetHashCode(MemberExpressionCacheKey obj)
         {
-            var hashCodeCombiner = new HashCodeCombiner();
+            var hashCodeCombiner = new HashCode();
             hashCodeCombiner.Add(obj.ModelType);
 
             foreach (var member in obj)
@@ -47,7 +48,7 @@ namespace Microsoft.AspNetCore.Mvc.ViewFeatures
                 hashCodeCombiner.Add(member);
             }
 
-            return hashCodeCombiner.CombinedHash;
+            return hashCodeCombiner.ToHashCode();
         }
     }
 }

src/Shared/ClosedGenericMatcher/ClosedGenericMatcher.cs

@@ -1,8 +1,9 @@
 // Copyright (c) .NET Foundation. All rights reserved.
 // Licensed under the Apache License, Version 2.0. See License.txt in the project root for license information.
 
+#nullable enable
+
 using System;
-using System.Linq;
 using System.Reflection;
 
 namespace Microsoft.Extensions.Internal
@@ -28,7 +29,7 @@ namespace Microsoft.Extensions.Internal
         /// <c>typeof(KeyValuePair{,})</c>, and <paramref name="queryType"/> is
         /// <c>typeof(KeyValuePair{string, object})</c>.
         /// </remarks>
-        public static Type ExtractGenericInterface(Type queryType, Type interfaceType)
+        public static Type? ExtractGenericInterface(Type queryType, Type interfaceType)
         {
             if (queryType == null)
             {
@@ -62,9 +63,9 @@ namespace Microsoft.Extensions.Internal
                 candidate.GetGenericTypeDefinition() == interfaceType;
         }
 
-        private static Type GetGenericInstantiation(Type queryType, Type interfaceType)
+        private static Type? GetGenericInstantiation(Type queryType, Type interfaceType)
         {
-            Type bestMatch = null;
+            Type? bestMatch = null;
             var interfaces = queryType.GetInterfaces();
             foreach (var @interface in interfaces)
             {
@@ -103,4 +104,4 @@ namespace Microsoft.Extensions.Internal
             }
         }
     }
-}
+}