Add nullability to Localization (#22323)

* Changes to support nullable for ns2.0
* Change ref assembly project to use nullable context

eng/targets/CSharp.Common.targets

@@ -28,6 +28,17 @@
     </ItemGroup>
   </Target>
 
+  <Choose>
+    <When Condition="'$(Nullable)' != '' AND ('$(TargetFramework)' == 'netstandard2.0' OR '$(TargetFrameworkIdentifier)' == '.NETFramework')">
+        <PropertyGroup>
+          <DefineConstants>$(DefineConstants),INTERNAL_NULLABLE_ATTRIBUTES</DefineConstants>
+        </PropertyGroup>
+        <ItemGroup>
+          <Compile Include="$(SharedSourceRoot)Nullable\NullableAttributes.cs" />
+        </ItemGroup>
+    </When>
+  </Choose>
+
   <Import Project="Packaging.targets" />
   <Import Project="ResolveReferences.targets" />
 

eng/targets/ReferenceAssembly.targets

@@ -26,11 +26,12 @@
       <_TargetFrameworkOverride />
       <_TargetFrameworkOverride
           Condition=" @(_ResultTargetFramework->Count()) > 1 ">%0A    &lt;TargetFrameworks Condition="'%24(DotNetBuildFromSource)' == 'true'"&gt;%24(DefaultNetCoreTargetFramework)&lt;/TargetFrameworks&gt;</_TargetFrameworkOverride>
+      <_NullableProperty Condition="'$(Nullable)' != ''">%0A    &lt;Nullable&gt;annotations&lt;/Nullable&gt;</_NullableProperty>
       <ProjectListContentLines><![CDATA[
 <!-- This file is automatically generated. -->
 <Project Sdk="Microsoft.NET.Sdk">
   <PropertyGroup>
-    <TargetFrameworks>@(_ResultTargetFramework)</TargetFrameworks>$(_TargetFrameworkOverride)
+    <TargetFrameworks>@(_ResultTargetFramework)</TargetFrameworks>$(_TargetFrameworkOverride)$(_NullableProperty)
   </PropertyGroup>
   @(ProjectListContentItem->'%(Identity)', '%0A')
 </Project>

src/Localization/Abstractions/ref/Microsoft.Extensions.Localization.Abstractions.csproj

@@ -3,6 +3,7 @@
   <PropertyGroup>
     <TargetFrameworks>netstandard2.0;$(DefaultNetCoreTargetFramework)</TargetFrameworks>
     <TargetFrameworks Condition="'$(DotNetBuildFromSource)' == 'true'">$(DefaultNetCoreTargetFramework)</TargetFrameworks>
+    <Nullable>annotations</Nullable>
   </PropertyGroup>
   <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
     <Compile Include="Microsoft.Extensions.Localization.Abstractions.netstandard2.0.cs" />

src/Localization/Abstractions/ref/Microsoft.Extensions.Localization.Abstractions.netcoreapp.cs

@@ -21,10 +21,10 @@ namespace Microsoft.Extensions.Localization
     {
         public LocalizedString(string name, string value) { }
         public LocalizedString(string name, string value, bool resourceNotFound) { }
-        public LocalizedString(string name, string value, bool resourceNotFound, string searchedLocation) { }
+        public LocalizedString(string name, string value, bool resourceNotFound, string? searchedLocation) { }
         public string Name { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
         public bool ResourceNotFound { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
-        public string SearchedLocation { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
+        public string? SearchedLocation { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
         public string Value { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
         public static implicit operator string (Microsoft.Extensions.Localization.LocalizedString localizedString) { throw null; }
         public override string ToString() { throw null; }

src/Localization/Abstractions/ref/Microsoft.Extensions.Localization.Abstractions.netstandard2.0.cs

@@ -21,10 +21,10 @@ namespace Microsoft.Extensions.Localization
     {
         public LocalizedString(string name, string value) { }
         public LocalizedString(string name, string value, bool resourceNotFound) { }
-        public LocalizedString(string name, string value, bool resourceNotFound, string searchedLocation) { }
+        public LocalizedString(string name, string value, bool resourceNotFound, string? searchedLocation) { }
         public string Name { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
         public bool ResourceNotFound { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
-        public string SearchedLocation { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
+        public string? SearchedLocation { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
         public string Value { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
         public static implicit operator string (Microsoft.Extensions.Localization.LocalizedString localizedString) { throw null; }
         public override string ToString() { throw null; }

src/Localization/Abstractions/src/LocalizedString.cs

@@ -38,7 +38,7 @@ namespace Microsoft.Extensions.Localization
         /// <param name="value">The actual string.</param>
         /// <param name="resourceNotFound">Whether the string was not found in a resource. Set this to <c>true</c> to indicate an alternate string value was used.</param>
         /// <param name="searchedLocation">The location which was searched for a localization value.</param>
-        public LocalizedString(string name, string value, bool resourceNotFound, string searchedLocation)
+        public LocalizedString(string name, string value, bool resourceNotFound, string? searchedLocation)
         {
             if (name == null)
             {
@@ -60,7 +60,7 @@ namespace Microsoft.Extensions.Localization
         /// Implicitly converts the <see cref="LocalizedString"/> to a <see cref="string"/>.
         /// </summary>
         /// <param name="localizedString">The string to be implicitly converted.</param>
-        public static implicit operator string(LocalizedString localizedString)
+        public static implicit operator string?(LocalizedString localizedString)
         {
             return localizedString?.Value;
         }
@@ -83,7 +83,7 @@ namespace Microsoft.Extensions.Localization
         /// <summary>
         /// The location which was searched for a localization value.
         /// </summary>
-        public string SearchedLocation { get; }
+        public string? SearchedLocation { get; }
 
         /// <summary>
         /// Returns the actual string.

src/Localization/Abstractions/src/Microsoft.Extensions.Localization.Abstractions.csproj

@@ -13,6 +13,7 @@ Microsoft.Extensions.Localization.IStringLocalizer&lt;T&gt;</Description>
     <PackageTags>localization</PackageTags>
     <IsPackable>true</IsPackable>
     <IsAspNetCoreApp>true</IsAspNetCoreApp>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
 </Project>

src/Localization/Localization/ref/Microsoft.Extensions.Localization.csproj

@@ -3,6 +3,7 @@
   <PropertyGroup>
     <TargetFrameworks>netstandard2.0;$(DefaultNetCoreTargetFramework)</TargetFrameworks>
     <TargetFrameworks Condition="'$(DotNetBuildFromSource)' == 'true'">$(DefaultNetCoreTargetFramework)</TargetFrameworks>
+    <Nullable>annotations</Nullable>
   </PropertyGroup>
   <ItemGroup Condition="'$(TargetFramework)' == 'netstandard2.0'">
     <Compile Include="Microsoft.Extensions.Localization.netstandard2.0.cs" />

src/Localization/Localization/ref/Microsoft.Extensions.Localization.netcoreapp.cs

@@ -13,7 +13,7 @@ namespace Microsoft.Extensions.Localization
 {
     public partial interface IResourceNamesCache
     {
-        System.Collections.Generic.IList<string> GetOrAdd(string name, System.Func<string, System.Collections.Generic.IList<string>> valueFactory);
+        System.Collections.Generic.IList<string>? GetOrAdd(string name, System.Func<string, System.Collections.Generic.IList<string>?> valueFactory);
     }
     public partial class LocalizationOptions
     {
@@ -35,7 +35,7 @@ namespace Microsoft.Extensions.Localization
         public virtual Microsoft.Extensions.Localization.LocalizedString this[string name, params object[] arguments] { get { throw null; } }
         public virtual System.Collections.Generic.IEnumerable<Microsoft.Extensions.Localization.LocalizedString> GetAllStrings(bool includeParentCultures) { throw null; }
         protected System.Collections.Generic.IEnumerable<Microsoft.Extensions.Localization.LocalizedString> GetAllStrings(bool includeParentCultures, System.Globalization.CultureInfo culture) { throw null; }
-        protected string GetStringSafely(string name, System.Globalization.CultureInfo culture) { throw null; }
+        protected string? GetStringSafely(string name, System.Globalization.CultureInfo? culture) { throw null; }
     }
     public partial class ResourceManagerStringLocalizerFactory : Microsoft.Extensions.Localization.IStringLocalizerFactory
     {
@@ -43,17 +43,17 @@ namespace Microsoft.Extensions.Localization
         public Microsoft.Extensions.Localization.IStringLocalizer Create(string baseName, string location) { throw null; }
         public Microsoft.Extensions.Localization.IStringLocalizer Create(System.Type resourceSource) { throw null; }
         protected virtual Microsoft.Extensions.Localization.ResourceManagerStringLocalizer CreateResourceManagerStringLocalizer(System.Reflection.Assembly assembly, string baseName) { throw null; }
-        protected virtual Microsoft.Extensions.Localization.ResourceLocationAttribute GetResourceLocationAttribute(System.Reflection.Assembly assembly) { throw null; }
+        protected virtual Microsoft.Extensions.Localization.ResourceLocationAttribute? GetResourceLocationAttribute(System.Reflection.Assembly assembly) { throw null; }
         protected virtual string GetResourcePrefix(System.Reflection.TypeInfo typeInfo) { throw null; }
-        protected virtual string GetResourcePrefix(System.Reflection.TypeInfo typeInfo, string baseNamespace, string resourcesRelativePath) { throw null; }
+        protected virtual string GetResourcePrefix(System.Reflection.TypeInfo typeInfo, string? baseNamespace, string? resourcesRelativePath) { throw null; }
         protected virtual string GetResourcePrefix(string baseResourceName, string baseNamespace) { throw null; }
         protected virtual string GetResourcePrefix(string location, string baseName, string resourceLocation) { throw null; }
-        protected virtual Microsoft.Extensions.Localization.RootNamespaceAttribute GetRootNamespaceAttribute(System.Reflection.Assembly assembly) { throw null; }
+        protected virtual Microsoft.Extensions.Localization.RootNamespaceAttribute? GetRootNamespaceAttribute(System.Reflection.Assembly assembly) { throw null; }
     }
     public partial class ResourceNamesCache : Microsoft.Extensions.Localization.IResourceNamesCache
     {
         public ResourceNamesCache() { }
-        public System.Collections.Generic.IList<string> GetOrAdd(string name, System.Func<string, System.Collections.Generic.IList<string>> valueFactory) { throw null; }
+        public System.Collections.Generic.IList<string>? GetOrAdd(string name, System.Func<string, System.Collections.Generic.IList<string>?> valueFactory) { throw null; }
     }
     [System.AttributeUsageAttribute(System.AttributeTargets.Assembly, AllowMultiple=false, Inherited=false)]
     public partial class RootNamespaceAttribute : System.Attribute
@@ -69,15 +69,15 @@ namespace Microsoft.Extensions.Localization.Internal
         public AssemblyWrapper(System.Reflection.Assembly assembly) { }
         public System.Reflection.Assembly Assembly { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
         public virtual string FullName { get { throw null; } }
-        public virtual System.IO.Stream GetManifestResourceStream(string name) { throw null; }
+        public virtual System.IO.Stream? GetManifestResourceStream(string name) { throw null; }
     }
     public partial interface IResourceStringProvider
     {
-        System.Collections.Generic.IList<string> GetAllResourceStrings(System.Globalization.CultureInfo culture, bool throwOnMissing);
+        System.Collections.Generic.IList<string>? GetAllResourceStrings(System.Globalization.CultureInfo culture, bool throwOnMissing);
     }
     public partial class ResourceManagerStringProvider : Microsoft.Extensions.Localization.Internal.IResourceStringProvider
     {
         public ResourceManagerStringProvider(Microsoft.Extensions.Localization.IResourceNamesCache resourceCache, System.Resources.ResourceManager resourceManager, System.Reflection.Assembly assembly, string baseName) { }
-        public System.Collections.Generic.IList<string> GetAllResourceStrings(System.Globalization.CultureInfo culture, bool throwOnMissing) { throw null; }
+        public System.Collections.Generic.IList<string>? GetAllResourceStrings(System.Globalization.CultureInfo culture, bool throwOnMissing) { throw null; }
     }
 }

src/Localization/Localization/ref/Microsoft.Extensions.Localization.netstandard2.0.cs

@@ -13,7 +13,7 @@ namespace Microsoft.Extensions.Localization
 {
     public partial interface IResourceNamesCache
     {
-        System.Collections.Generic.IList<string> GetOrAdd(string name, System.Func<string, System.Collections.Generic.IList<string>> valueFactory);
+        System.Collections.Generic.IList<string>? GetOrAdd(string name, System.Func<string, System.Collections.Generic.IList<string>?> valueFactory);
     }
     public partial class LocalizationOptions
     {
@@ -35,7 +35,7 @@ namespace Microsoft.Extensions.Localization
         public virtual Microsoft.Extensions.Localization.LocalizedString this[string name, params object[] arguments] { get { throw null; } }
         public virtual System.Collections.Generic.IEnumerable<Microsoft.Extensions.Localization.LocalizedString> GetAllStrings(bool includeParentCultures) { throw null; }
         protected System.Collections.Generic.IEnumerable<Microsoft.Extensions.Localization.LocalizedString> GetAllStrings(bool includeParentCultures, System.Globalization.CultureInfo culture) { throw null; }
-        protected string GetStringSafely(string name, System.Globalization.CultureInfo culture) { throw null; }
+        protected string? GetStringSafely(string name, System.Globalization.CultureInfo? culture) { throw null; }
     }
     public partial class ResourceManagerStringLocalizerFactory : Microsoft.Extensions.Localization.IStringLocalizerFactory
     {
@@ -43,17 +43,17 @@ namespace Microsoft.Extensions.Localization
         public Microsoft.Extensions.Localization.IStringLocalizer Create(string baseName, string location) { throw null; }
         public Microsoft.Extensions.Localization.IStringLocalizer Create(System.Type resourceSource) { throw null; }
         protected virtual Microsoft.Extensions.Localization.ResourceManagerStringLocalizer CreateResourceManagerStringLocalizer(System.Reflection.Assembly assembly, string baseName) { throw null; }
-        protected virtual Microsoft.Extensions.Localization.ResourceLocationAttribute GetResourceLocationAttribute(System.Reflection.Assembly assembly) { throw null; }
+        protected virtual Microsoft.Extensions.Localization.ResourceLocationAttribute? GetResourceLocationAttribute(System.Reflection.Assembly assembly) { throw null; }
         protected virtual string GetResourcePrefix(System.Reflection.TypeInfo typeInfo) { throw null; }
-        protected virtual string GetResourcePrefix(System.Reflection.TypeInfo typeInfo, string baseNamespace, string resourcesRelativePath) { throw null; }
+        protected virtual string GetResourcePrefix(System.Reflection.TypeInfo typeInfo, string? baseNamespace, string? resourcesRelativePath) { throw null; }
         protected virtual string GetResourcePrefix(string baseResourceName, string baseNamespace) { throw null; }
         protected virtual string GetResourcePrefix(string location, string baseName, string resourceLocation) { throw null; }
-        protected virtual Microsoft.Extensions.Localization.RootNamespaceAttribute GetRootNamespaceAttribute(System.Reflection.Assembly assembly) { throw null; }
+        protected virtual Microsoft.Extensions.Localization.RootNamespaceAttribute? GetRootNamespaceAttribute(System.Reflection.Assembly assembly) { throw null; }
     }
     public partial class ResourceNamesCache : Microsoft.Extensions.Localization.IResourceNamesCache
     {
         public ResourceNamesCache() { }
-        public System.Collections.Generic.IList<string> GetOrAdd(string name, System.Func<string, System.Collections.Generic.IList<string>> valueFactory) { throw null; }
+        public System.Collections.Generic.IList<string>? GetOrAdd(string name, System.Func<string, System.Collections.Generic.IList<string>?> valueFactory) { throw null; }
     }
     [System.AttributeUsageAttribute(System.AttributeTargets.Assembly, AllowMultiple=false, Inherited=false)]
     public partial class RootNamespaceAttribute : System.Attribute
@@ -69,15 +69,15 @@ namespace Microsoft.Extensions.Localization.Internal
         public AssemblyWrapper(System.Reflection.Assembly assembly) { }
         public System.Reflection.Assembly Assembly { [System.Runtime.CompilerServices.CompilerGeneratedAttribute] get { throw null; } }
         public virtual string FullName { get { throw null; } }
-        public virtual System.IO.Stream GetManifestResourceStream(string name) { throw null; }
+        public virtual System.IO.Stream? GetManifestResourceStream(string name) { throw null; }
     }
     public partial interface IResourceStringProvider
     {
-        System.Collections.Generic.IList<string> GetAllResourceStrings(System.Globalization.CultureInfo culture, bool throwOnMissing);
+        System.Collections.Generic.IList<string>? GetAllResourceStrings(System.Globalization.CultureInfo culture, bool throwOnMissing);
     }
     public partial class ResourceManagerStringProvider : Microsoft.Extensions.Localization.Internal.IResourceStringProvider
     {
         public ResourceManagerStringProvider(Microsoft.Extensions.Localization.IResourceNamesCache resourceCache, System.Resources.ResourceManager resourceManager, System.Reflection.Assembly assembly, string baseName) { }
-        public System.Collections.Generic.IList<string> GetAllResourceStrings(System.Globalization.CultureInfo culture, bool throwOnMissing) { throw null; }
+        public System.Collections.Generic.IList<string>? GetAllResourceStrings(System.Globalization.CultureInfo culture, bool throwOnMissing) { throw null; }
     }
 }

src/Localization/Localization/src/IResourceNamesCache.cs

@@ -17,6 +17,6 @@ namespace Microsoft.Extensions.Localization
         /// <param name="name">The resource name to add string names for.</param>
         /// <param name="valueFactory">The function used to generate the string names for the resource.</param>
         /// <returns>The string names for the resource.</returns>
-        IList<string> GetOrAdd(string name, Func<string, IList<string>> valueFactory);
+        IList<string>? GetOrAdd(string name, Func<string, IList<string>?> valueFactory);
     }
 }

src/Localization/Localization/src/Internal/AssemblyWrapper.cs

@@ -25,8 +25,8 @@ namespace Microsoft.Extensions.Localization.Internal
 
         public Assembly Assembly { get; }
 
-        public virtual string FullName => Assembly.FullName;
+        public virtual string FullName => Assembly.FullName!;
 
-        public virtual Stream GetManifestResourceStream(string name) => Assembly.GetManifestResourceStream(name);
+        public virtual Stream? GetManifestResourceStream(string name) => Assembly.GetManifestResourceStream(name);
     }
 }

src/Localization/Localization/src/Internal/IResourceStringProvider.cs

@@ -1,4 +1,4 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// 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.Collections.Generic;
@@ -12,6 +12,6 @@ namespace Microsoft.Extensions.Localization.Internal
     /// </summary>
     public interface IResourceStringProvider
     {
-        IList<string> GetAllResourceStrings(CultureInfo culture, bool throwOnMissing);
+        IList<string>? GetAllResourceStrings(CultureInfo culture, bool throwOnMissing);
     }
 }

src/Localization/Localization/src/Internal/ResourceManagerStringLocalizerLoggerExtensions.cs

@@ -9,7 +9,7 @@ namespace Microsoft.Extensions.Localization.Internal
 {
     internal static class ResourceManagerStringLocalizerLoggerExtensions
     {
-        private static readonly Action<ILogger, string, string, CultureInfo, Exception> _searchedLocation;
+        private static readonly Action<ILogger, string, string, CultureInfo, Exception?> _searchedLocation;
 
         static ResourceManagerStringLocalizerLoggerExtensions()
         {

src/Localization/Localization/src/Internal/ResourceManagerStringProvider.cs

@@ -1,4 +1,4 @@
-// Copyright (c) .NET Foundation. All rights reserved.
+// 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.Collections;
@@ -51,7 +51,7 @@ namespace Microsoft.Extensions.Localization.Internal
             return resourceStreamName;
         }
 
-        public IList<string> GetAllResourceStrings(CultureInfo culture, bool throwOnMissing)
+        public IList<string>? GetAllResourceStrings(CultureInfo culture, bool throwOnMissing)
         {
             var cacheKey = GetResourceCacheKey(culture);
 
@@ -72,9 +72,12 @@ namespace Microsoft.Extensions.Localization.Internal
                 }
 
                 var names = new List<string>();
-                foreach (DictionaryEntry entry in resourceSet)
+                foreach (DictionaryEntry? entry in resourceSet)
                 {
-                    names.Add((string)entry.Key);
+                    if (entry?.Key is string key)
+                    {
+                        names.Add(key);
+                    }
                 }
 
                 return names;

src/Localization/Localization/src/Microsoft.Extensions.Localization.csproj

@@ -10,6 +10,7 @@
     <PackageTags>localization</PackageTags>
     <IsPackable>true</IsPackable>
     <IsAspNetCoreApp>true</IsAspNetCoreApp>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>

src/Localization/Localization/src/ResourceManagerStringLocalizer.cs

@@ -5,6 +5,7 @@ using System;
 using System.Collections.Concurrent;
 using System.Collections.Generic;
 using System.Globalization;
+using System.Linq;
 using System.Reflection;
 using System.Resources;
 using Microsoft.Extensions.Localization.Internal;
@@ -19,7 +20,7 @@ namespace Microsoft.Extensions.Localization
     /// <remarks>This type is thread-safe.</remarks>
     public class ResourceManagerStringLocalizer : IStringLocalizer
     {
-        private readonly ConcurrentDictionary<string, object> _missingManifestCache = new ConcurrentDictionary<string, object>();
+        private readonly ConcurrentDictionary<string, object?> _missingManifestCache = new ConcurrentDictionary<string, object?>();
         private readonly IResourceNamesCache _resourceNamesCache;
         private readonly ResourceManager _resourceManager;
         private readonly IResourceStringProvider _resourceStringProvider;
@@ -171,7 +172,7 @@ namespace Microsoft.Extensions.Localization
                 ? GetResourceNamesFromCultureHierarchy(culture)
                 : _resourceStringProvider.GetAllResourceStrings(culture, true);
 
-            foreach (var name in resourceNames)
+            foreach (var name in resourceNames ?? Enumerable.Empty<string>())
             {
                 var value = GetStringSafely(name, culture);
                 yield return new LocalizedString(name, value ?? name, resourceNotFound: value == null, searchedLocation: _resourceBaseName);
@@ -185,7 +186,7 @@ namespace Microsoft.Extensions.Localization
         /// <param name="name">The name of the string resource.</param>
         /// <param name="culture">The <see cref="CultureInfo"/> to get the string for.</param>
         /// <returns>The resource string, or <c>null</c> if none was found.</returns>
-        protected string GetStringSafely(string name, CultureInfo culture)
+        protected string? GetStringSafely(string name, CultureInfo? culture)
         {
             if (name == null)
             {

src/Localization/Localization/src/ResourceManagerStringLocalizerFactory.cs

@@ -82,7 +82,7 @@ namespace Microsoft.Extensions.Localization
         /// For the type "Sample.Controllers.Home" if there's a resourceRelativePath return
         /// "Sample.Resourcepath.Controllers.Home" if there isn't one then it would return "Sample.Controllers.Home".
         /// </remarks>
-        protected virtual string GetResourcePrefix(TypeInfo typeInfo, string baseNamespace, string resourcesRelativePath)
+        protected virtual string GetResourcePrefix(TypeInfo typeInfo, string? baseNamespace, string? resourcesRelativePath)
         {
             if (typeInfo == null)
             {
@@ -94,6 +94,11 @@ namespace Microsoft.Extensions.Localization
                 throw new ArgumentNullException(nameof(baseNamespace));
             }
 
+            if (string.IsNullOrEmpty(typeInfo.FullName))
+            {
+                throw new ArgumentException(Resources.FormatLocalization_TypeMustHaveTypeName(typeInfo));
+            }
+
             if (string.IsNullOrEmpty(resourcesRelativePath))
             {
                 return typeInfo.FullName;
@@ -219,7 +224,7 @@ namespace Microsoft.Extensions.Localization
         /// <param name="assembly">The assembly to get a <see cref="ResourceLocationAttribute"/> from.</param>
         /// <returns>The <see cref="ResourceLocationAttribute"/> associated with the given <see cref="Assembly"/>.</returns>
         /// <remarks>This method is protected and virtual for testing purposes only.</remarks>
-        protected virtual ResourceLocationAttribute GetResourceLocationAttribute(Assembly assembly)
+        protected virtual ResourceLocationAttribute? GetResourceLocationAttribute(Assembly assembly)
         {
             return assembly.GetCustomAttribute<ResourceLocationAttribute>();
         }
@@ -228,17 +233,21 @@ namespace Microsoft.Extensions.Localization
         /// <param name="assembly">The assembly to get a <see cref="RootNamespaceAttribute"/> from.</param>
         /// <returns>The <see cref="RootNamespaceAttribute"/> associated with the given <see cref="Assembly"/>.</returns>
         /// <remarks>This method is protected and virtual for testing purposes only.</remarks>
-        protected virtual RootNamespaceAttribute GetRootNamespaceAttribute(Assembly assembly)
+        protected virtual RootNamespaceAttribute? GetRootNamespaceAttribute(Assembly assembly)
         {
             return assembly.GetCustomAttribute<RootNamespaceAttribute>();
         }
 
-        private string GetRootNamespace(Assembly assembly)
+        private string? GetRootNamespace(Assembly assembly)
         {
             var rootNamespaceAttribute = GetRootNamespaceAttribute(assembly);
 
-            return rootNamespaceAttribute?.RootNamespace ??
+            if (rootNamespaceAttribute != null)
-                new AssemblyName(assembly.FullName).Name;
+            {
+                return rootNamespaceAttribute.RootNamespace;
+            }
+
+            return assembly.GetName().Name;
         }
 
         private string GetResourcePath(Assembly assembly)
@@ -256,7 +265,7 @@ namespace Microsoft.Extensions.Localization
             return resourceLocation;
         }
 
-        private static string TrimPrefix(string name, string prefix)
+        private static string? TrimPrefix(string name, string prefix)
         {
             if (name.StartsWith(prefix, StringComparison.Ordinal))
             {

src/Localization/Localization/src/ResourceNamesCache.cs

@@ -12,7 +12,7 @@ namespace Microsoft.Extensions.Localization
     /// </summary>
     public class ResourceNamesCache : IResourceNamesCache
     {
-        private readonly ConcurrentDictionary<string, IList<string>> _cache = new ConcurrentDictionary<string, IList<string>>();
+        private readonly ConcurrentDictionary<string, IList<string>?> _cache = new ConcurrentDictionary<string, IList<string>?>();
 
         /// <summary>
         /// Creates a new <see cref="ResourceNamesCache" />
@@ -22,7 +22,7 @@ namespace Microsoft.Extensions.Localization
         }
 
         /// <inheritdoc />
-        public IList<string> GetOrAdd(string name, Func<string, IList<string>> valueFactory)
+        public IList<string>? GetOrAdd(string name, Func<string, IList<string>?> valueFactory)
         {
             return _cache.GetOrAdd(name, valueFactory);
         }

src/Localization/Localization/src/Resources.resx

@@ -123,4 +123,7 @@
   <data name="Localization_MissingManifest_Parent" xml:space="preserve">
     <value>No manifests exist for the current culture.</value>
   </data>
+  <data name="Localization_TypeMustHaveTypeName" xml:space="preserve">
+    <value>Type '{0}' must have a non-null type name.</value>
+  </data>
 </root>

src/Localization/Localization/test/Microsoft.Extensions.Localization.RootNamespace.Tests/Microsoft.Extensions.Localization.RootNamespace.Tests.csproj

@@ -2,6 +2,7 @@
   <PropertyGroup>
     <TargetFrameworks>$(DefaultNetCoreTargetFramework);net472</TargetFrameworks>
     <RootNamespace>LocalizationTest.Abc</RootNamespace>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
   <ItemGroup>
     <Compile Remove="NewFolder\**" />

src/Localization/Localization/test/Microsoft.Extensions.Localization.Tests/Microsoft.Extensions.Localization.Tests.csproj

@@ -2,6 +2,7 @@
 
   <PropertyGroup>
     <TargetFrameworks>$(DefaultNetCoreTargetFramework);net472</TargetFrameworks>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>

src/Localization/Localization/test/Microsoft.Extensions.Localization.Tests/ResourceManagerStringLocalizerFactoryTest.cs

@@ -1,6 +1,7 @@
-// Copyright (c) .NET Foundation. All rights reserved. 
+// 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 disable
 using System;
 using System.IO;
 using System.Reflection;
@@ -84,7 +85,7 @@ namespace Microsoft.Extensions.Localization.Tests
 
             // Assert
             Assert.Equal(typeFactory.BaseName, stringFactory.BaseName);
-            Assert.Equal(typeFactory.Assembly.FullName, stringFactory.Assembly.FullName);
+            Assert.Equal(typeFactory.Assembly!.FullName, stringFactory.Assembly!.FullName);
         }
 
         [Fact]
@@ -293,7 +294,7 @@ namespace Microsoft.Extensions.Localization.Tests
             var factory = new ResourceManagerStringLocalizerFactory(localizationOptions: options.Object, loggerFactory: loggerFactory);
 
             // Act & Assert
-            Assert.Throws<ArgumentNullException>(() => factory.Create("baseName", location: null));
+            Assert.Throws<ArgumentNullException>(() => factory.Create("baseName", location: null!));
         }
     }
 }

src/Localization/Localization/test/Microsoft.Extensions.Localization.Tests/ResourceManagerStringLocalizerTest.cs

@@ -249,9 +249,9 @@ namespace Microsoft.Extensions.Localization
                 _assemblyWrapper = assemblyWrapper;
             }
 
-            public override string GetString(string name, CultureInfo culture) => null;
+            public override string? GetString(string name, CultureInfo? culture) => null;
 
-            public override ResourceSet GetResourceSet(CultureInfo culture, bool createIfNotExists, bool tryParents)
+            public override ResourceSet? GetResourceSet(CultureInfo culture, bool createIfNotExists, bool tryParents)
             {
                 var resourceStream = _assemblyWrapper.GetManifestResourceStream(BaseName);
 
@@ -287,7 +287,7 @@ namespace Microsoft.Extensions.Localization
 
             public int ManifestResourceStreamCallCount { get; private set; }
 
-            public override Stream GetManifestResourceStream(string name)
+            public override Stream? GetManifestResourceStream(string name)
             {
                 ManifestResourceStreamCallCount++;
 

src/Localization/Localization/test/Microsoft.Extensions.Localization.Tests/StringLocalizerOfTTest.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 System.Globalization;
 using Moq;
 using Xunit;
 
@@ -15,7 +14,7 @@ namespace Microsoft.Extensions.Localization
         {
             // Arrange, act and assert
             var exception = Assert.Throws<ArgumentNullException>(
-                () => new StringLocalizer<object>(factory: null));
+                () => new StringLocalizer<object>(factory: null!));
 
             Assert.Equal("factory", exception.ParamName);
         }
@@ -45,7 +44,7 @@ namespace Microsoft.Extensions.Localization
             var localizer = new StringLocalizer<object>(factory.Object);
 
             // Act and assert
-            var exception = Assert.Throws<ArgumentNullException>(() => localizer[name: null]);
+            var exception = Assert.Throws<ArgumentNullException>(() => localizer[name: null!]);
 
             Assert.Equal("name", exception.ParamName);
         }
@@ -80,7 +79,7 @@ namespace Microsoft.Extensions.Localization
             var localizer = new StringLocalizer<object>(factory.Object);
 
             // Act and assert
-            var exception = Assert.Throws<ArgumentNullException>(() => localizer[name: null]);
+            var exception = Assert.Throws<ArgumentNullException>(() => localizer[name: null!]);
 
             Assert.Equal("name", exception.ParamName);
         }

src/Shared/Nullable/NullableAttributes.cs

@@ -0,0 +1,196 @@
+// Licensed to the .NET Foundation under one or more agreements.
+// The .NET Foundation licenses this file to you under the MIT license.
+// See the LICENSE file in the project root for more information.
+// From https://github.com/dotnet/runtime/blob/ef72b95937703e485fdbbb75f3251fedfd1a0ef9/src/libraries/System.Private.CoreLib/src/System/Diagnostics/CodeAnalysis/NullableAttributes.cs
+
+namespace System.Diagnostics.CodeAnalysis
+{
+    /// <summary>Specifies that null is allowed as an input even if the corresponding type disallows it.</summary>
+    [AttributeUsage(AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.Property, Inherited = false)]
+#if INTERNAL_NULLABLE_ATTRIBUTES
+    internal
+#else
+    public
+#endif
+        sealed class AllowNullAttribute : Attribute { }
+
+    /// <summary>Specifies that null is disallowed as an input even if the corresponding type allows it.</summary>
+    [AttributeUsage(AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.Property, Inherited = false)]
+#if INTERNAL_NULLABLE_ATTRIBUTES
+    internal
+#else
+    public
+#endif
+        sealed class DisallowNullAttribute : Attribute { }
+
+    /// <summary>Specifies that an output may be null even if the corresponding type disallows it.</summary>
+    [AttributeUsage(AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.Property | AttributeTargets.ReturnValue, Inherited = false)]
+#if INTERNAL_NULLABLE_ATTRIBUTES
+    internal
+#else
+    public
+#endif
+        sealed class MaybeNullAttribute : Attribute { }
+
+    /// <summary>Specifies that an output will not be null even if the corresponding type allows it. Specifies that an input argument was not null when the call returns.</summary>
+    [AttributeUsage(AttributeTargets.Field | AttributeTargets.Parameter | AttributeTargets.Property | AttributeTargets.ReturnValue, Inherited = false)]
+#if INTERNAL_NULLABLE_ATTRIBUTES
+    internal
+#else
+    public
+#endif
+        sealed class NotNullAttribute : Attribute { }
+
+    /// <summary>Specifies that when a method returns <see cref="ReturnValue"/>, the parameter may be null even if the corresponding type disallows it.</summary>
+    [AttributeUsage(AttributeTargets.Parameter, Inherited = false)]
+#if INTERNAL_NULLABLE_ATTRIBUTES
+    internal
+#else
+    public
+#endif
+        sealed class MaybeNullWhenAttribute : Attribute
+    {
+        /// <summary>Initializes the attribute with the specified return value condition.</summary>
+        /// <param name="returnValue">
+        /// The return value condition. If the method returns this value, the associated parameter may be null.
+        /// </param>
+        public MaybeNullWhenAttribute(bool returnValue) => ReturnValue = returnValue;
+
+        /// <summary>Gets the return value condition.</summary>
+        public bool ReturnValue { get; }
+    }
+
+    /// <summary>Specifies that when a method returns <see cref="ReturnValue"/>, the parameter will not be null even if the corresponding type allows it.</summary>
+    [AttributeUsage(AttributeTargets.Parameter, Inherited = false)]
+#if INTERNAL_NULLABLE_ATTRIBUTES
+    internal
+#else
+    public
+#endif
+        sealed class NotNullWhenAttribute : Attribute
+    {
+        /// <summary>Initializes the attribute with the specified return value condition.</summary>
+        /// <param name="returnValue">
+        /// The return value condition. If the method returns this value, the associated parameter will not be null.
+        /// </param>
+        public NotNullWhenAttribute(bool returnValue) => ReturnValue = returnValue;
+
+        /// <summary>Gets the return value condition.</summary>
+        public bool ReturnValue { get; }
+    }
+
+    /// <summary>Specifies that the output will be non-null if the named parameter is non-null.</summary>
+    [AttributeUsage(AttributeTargets.Parameter | AttributeTargets.Property | AttributeTargets.ReturnValue, AllowMultiple = true, Inherited = false)]
+#if INTERNAL_NULLABLE_ATTRIBUTES
+    internal
+#else
+    public
+#endif
+        sealed class NotNullIfNotNullAttribute : Attribute
+    {
+        /// <summary>Initializes the attribute with the associated parameter name.</summary>
+        /// <param name="parameterName">
+        /// The associated parameter name.  The output will be non-null if the argument to the parameter specified is non-null.
+        /// </param>
+        public NotNullIfNotNullAttribute(string parameterName) => ParameterName = parameterName;
+
+        /// <summary>Gets the associated parameter name.</summary>
+        public string ParameterName { get; }
+    }
+
+    /// <summary>Applied to a method that will never return under any circumstance.</summary>
+    [AttributeUsage(AttributeTargets.Method, Inherited = false)]
+#if INTERNAL_NULLABLE_ATTRIBUTES
+    internal
+#else
+    public
+#endif
+        sealed class DoesNotReturnAttribute : Attribute { }
+
+    /// <summary>Specifies that the method will not return if the associated Boolean parameter is passed the specified value.</summary>
+    [AttributeUsage(AttributeTargets.Parameter, Inherited = false)]
+#if INTERNAL_NULLABLE_ATTRIBUTES
+    internal
+#else
+    public
+#endif
+        sealed class DoesNotReturnIfAttribute : Attribute
+    {
+        /// <summary>Initializes the attribute with the specified parameter value.</summary>
+        /// <param name="parameterValue">
+        /// The condition parameter value. Code after the method will be considered unreachable by diagnostics if the argument to
+        /// the associated parameter matches this value.
+        /// </param>
+        public DoesNotReturnIfAttribute(bool parameterValue) => ParameterValue = parameterValue;
+
+        /// <summary>Gets the condition parameter value.</summary>
+        public bool ParameterValue { get; }
+    }
+
+    /// <summary>Specifies that the method or property will ensure that the listed field and property members have not-null values.</summary>
+    [AttributeUsage(AttributeTargets.Method | AttributeTargets.Property, Inherited = false, AllowMultiple = true)]
+#if INTERNAL_NULLABLE_ATTRIBUTES
+    internal
+#else
+    public
+#endif
+        sealed class MemberNotNullAttribute : Attribute
+    {
+        /// <summary>Initializes the attribute with a field or property member.</summary>
+        /// <param name="member">
+        /// The field or property member that is promised to be not-null.
+        /// </param>
+        public MemberNotNullAttribute(string member) => Members = new[] { member };
+
+        /// <summary>Initializes the attribute with the list of field and property members.</summary>
+        /// <param name="members">
+        /// The list of field and property members that are promised to be not-null.
+        /// </param>
+        public MemberNotNullAttribute(params string[] members) => Members = members;
+
+        /// <summary>Gets field or property member names.</summary>
+        public string[] Members { get; }
+    }
+
+    /// <summary>Specifies that the method or property will ensure that the listed field and property members have not-null values when returning with the specified return value condition.</summary>
+    [AttributeUsage(AttributeTargets.Method | AttributeTargets.Property, Inherited = false, AllowMultiple = true)]
+#if INTERNAL_NULLABLE_ATTRIBUTES
+    internal
+#else
+    public
+#endif
+        sealed class MemberNotNullWhenAttribute : Attribute
+    {
+        /// <summary>Initializes the attribute with the specified return value condition and a field or property member.</summary>
+        /// <param name="returnValue">
+        /// The return value condition. If the method returns this value, the associated parameter will not be null.
+        /// </param>
+        /// <param name="member">
+        /// The field or property member that is promised to be not-null.
+        /// </param>
+        public MemberNotNullWhenAttribute(bool returnValue, string member)
+        {
+            ReturnValue = returnValue;
+            Members = new[] { member };
+        }
+
+        /// <summary>Initializes the attribute with the specified return value condition and list of field and property members.</summary>
+        /// <param name="returnValue">
+        /// The return value condition. If the method returns this value, the associated parameter will not be null.
+        /// </param>
+        /// <param name="members">
+        /// The list of field and property members that are promised to be not-null.
+        /// </param>
+        public MemberNotNullWhenAttribute(bool returnValue, params string[] members)
+        {
+            ReturnValue = returnValue;
+            Members = members;
+        }
+
+        /// <summary>Gets the return value condition.</summary>
+        public bool ReturnValue { get; }
+
+        /// <summary>Gets field or property member names.</summary>
+        public string[] Members { get; }
+    }
+}