Fix warning when using nullable properties in ValidationMessageStore.Add field accessor

src/Components/Forms/src/PublicAPI.Unshipped.txt

@@ -1,4 +1,8 @@
 #nullable enable
+*REMOVED*Microsoft.AspNetCore.Components.Forms.ValidationMessageStore.Add(System.Linq.Expressions.Expression<System.Func<object!>!>! accessor, string! message) -> void
+*REMOVED*Microsoft.AspNetCore.Components.Forms.ValidationMessageStore.Add(System.Linq.Expressions.Expression<System.Func<object!>!>! accessor, System.Collections.Generic.IEnumerable<string!>! messages) -> void
+Microsoft.AspNetCore.Components.Forms.ValidationMessageStore.Add<TField>(System.Linq.Expressions.Expression<System.Func<TField>!>! accessor, string! message) -> void
+Microsoft.AspNetCore.Components.Forms.ValidationMessageStore.Add<TField>(System.Linq.Expressions.Expression<System.Func<TField>!>! accessor, System.Collections.Generic.IEnumerable<string!>! messages) -> void
 Microsoft.AspNetCore.Components.Forms.ValidationRequestedEventArgs.AddAsyncValidator(System.Func<System.Threading.CancellationToken, System.Threading.Tasks.Task!>! validator) -> void
 *REMOVED*static Microsoft.AspNetCore.Components.Forms.EditContextDataAnnotationsExtensions.AddDataAnnotationsValidation(this Microsoft.AspNetCore.Components.Forms.EditContext! editContext) -> Microsoft.AspNetCore.Components.Forms.EditContext!
 *REMOVED*static Microsoft.AspNetCore.Components.Forms.EditContextDataAnnotationsExtensions.EnableDataAnnotationsValidation(this Microsoft.AspNetCore.Components.Forms.EditContext! editContext) -> System.IDisposable!

src/Components/Forms/src/ValidationMessageStore.cs

@@ -35,7 +35,7 @@ public void Add(in FieldIdentifier fieldIdentifier, string message)
     /// </summary>
     /// <param name="accessor">Identifies the field for which to add the message.</param>
     /// <param name="message">The validation message.</param>
-    public void Add(Expression<Func<object>> accessor, string message)
+    public void Add<TField>(Expression<Func<TField>> accessor, string message)
         => Add(FieldIdentifier.Create(accessor), message);
 
     /// <summary>
@@ -51,7 +51,7 @@ public void Add(in FieldIdentifier fieldIdentifier, IEnumerable<string> messages
     /// </summary>
     /// <param name="accessor">Identifies the field for which to add the messages.</param>
     /// <param name="messages">The validation messages to be added.</param>
-    public void Add(Expression<Func<object>> accessor, IEnumerable<string> messages)
+    public void Add<TField>(Expression<Func<TField>> accessor, IEnumerable<string> messages)
         => Add(FieldIdentifier.Create(accessor), messages);
 
     /// <summary>

src/Components/Forms/test/ValidationMessageStoreTest.cs

@@ -89,4 +89,37 @@ public void CanClearMessagesForAllFields()
         Assert.Empty(messages[field1]);
         Assert.Empty(messages[field2]);
     }
+#nullable enable
+    [Fact]
+    public void CanAddMessagesUsingExpressionWithNullableProperty()
+    {
+        var model = new TestModel();
+        var editContext = new EditContext(model);
+        var messages = new ValidationMessageStore(editContext);
+
+        messages.Add(() => model.Text, "This value is not valid");
+
+        var fieldIdentifier = FieldIdentifier.Create(() => model.Text);
+        Assert.Equal(new[] { "This value is not valid" }, messages[fieldIdentifier]);
+    }
+
+    [Fact]
+    public void CanAddMultipleMessagesUsingExpressionWithNullableProperty()
+    {
+        var model = new TestModel();
+        var editContext = new EditContext(model);
+        var messages = new ValidationMessageStore(editContext);
+        var validationMessages = new[] { "First error", "Second error" };
+
+        messages.Add(() => model.Text, validationMessages);
+
+        var fieldIdentifier = FieldIdentifier.Create(() => model.Text);
+        Assert.Equal(validationMessages, messages[fieldIdentifier]);
+    }
+
+    private class TestModel
+    {
+        public string? Text { get; set; }
+    }
+#nullable disable
 }