Cannot set Dependency Property of the FontWeight? (Nullable<FontWeight>) type in XAML

Describe the bug

    public class MyControl : Control {
        public static readonly DependencyProperty NullableStructProperty = DependencyProperty.Register("NullableStruct", typeof(FontWeight?), typeof(MyControl), new PropertyMetadata(null));
        public FontWeight? NullableStruct { get { return (FontWeight?)GetValue(NullableStructProperty); } set { SetValue(NullableStructProperty, value); } }
    }

<local:MyControl x:Name="c3" NullableStruct="Bold"/>

Result: ‘XAML parsing failed.’ 'Failed to create a ‘Windows.Foundation.IReference`1<Windows.UI.Text.FontWeight>’ from the text ‘Bold’.

Reproduced in any version, including 1.0.0-preview2

Steps to reproduce the bug

Run sample App1.zip

Expected behavior

No response

Screenshots

No response

NuGet package version

WinUI 3 - Windows App SDK 0.8: 0.8.0 (If you’re seeing your issue in older previews of WinUI 3, please try this release)

Windows app type

• UWP
• Win32

Device form factor

Desktop

Windows version

May 2021 Update (19043)

Additional context

No response

[alexdi220]

It doesn’t work for non-dependency (simple) properties too:

public FontWeight? FontWeight { get; set; }

<local:MyStyle FontWeight="Bold"/> <!-- cause exception -->

[RealTommyKlein]

This looks like a bug where the framework doesn’t support unboxing FontWeight from a string (for MSFT employees, this code needs a valueString case to create a FontWeight from a string).