Make AddComponentReferenceCapture delegate non-null (#24842)

* Make the sample nullable enabled

Fixes https://github.com/dotnet/aspnetcore/issues/24794

src/Components/Components/src/RenderTree/RenderTreeFrameArrayBuilder.cs

@@ -104,7 +104,7 @@ namespace Microsoft.AspNetCore.Components.RenderTree
             };
         }
 
-        public void AppendComponentReferenceCapture(int sequence, Action<object?> componentReferenceCaptureAction, int parentFrameIndexValue)
+        public void AppendComponentReferenceCapture(int sequence, Action<object> componentReferenceCaptureAction, int parentFrameIndexValue)
         {
             if (_itemsInUse == _items.Length)
             {

src/Components/Components/src/Rendering/RenderTreeBuilder.cs

@@ -586,7 +586,7 @@ namespace Microsoft.AspNetCore.Components.Rendering
         /// </summary>
         /// <param name="sequence">An integer that represents the position of the instruction in the source code.</param>
         /// <param name="componentReferenceCaptureAction">An action to be invoked whenever the reference value changes.</param>
-        public void AddComponentReferenceCapture(int sequence, Action<object?> componentReferenceCaptureAction)
+        public void AddComponentReferenceCapture(int sequence, Action<object> componentReferenceCaptureAction)
         {
             var parentFrameIndex = GetCurrentParentFrameIndex();
             if (!parentFrameIndex.HasValue)

src/Components/Samples/BlazorServerApp/BlazorServerApp.csproj

@@ -3,6 +3,7 @@
   <PropertyGroup>
     <TargetFramework>$(DefaultNetCoreTargetFramework)</TargetFramework>
     <IsShippingPackage>false</IsShippingPackage>
+    <Nullable>enable</Nullable>
   </PropertyGroup>
 
   <ItemGroup>

src/Components/Samples/BlazorServerApp/Data/WeatherForecast.cs

@@ -10,6 +10,6 @@ namespace BlazorServerApp.Data
 
         public int TemperatureF => 32 + (int)(TemperatureC / 0.5556);
 
-        public string Summary { get; set; }
+        public string Summary { get; set; } = default!;
     }
 }

src/Components/Samples/BlazorServerApp/Pages/FetchData.razor

@@ -37,7 +37,7 @@ else
 }
 
 @code {
-    WeatherForecast[] forecasts;
+    WeatherForecast[]? forecasts;
 
     protected override async Task OnInitializedAsync()
     {

src/Components/Samples/BlazorServerApp/Shared/NavMenu.razor

@@ -28,7 +28,7 @@
 @code {
     bool collapseNavMenu = true;
 
-    string NavMenuCssClass => collapseNavMenu ? "collapse" : null;
+    string? NavMenuCssClass => collapseNavMenu ? "collapse" : null;
 
     void ToggleNavMenu()
     {