Setting FontFamily to null triggers a NullReferenceException

[MB-GA]

Describe the bug

If the FontFamily field on an element is set to null, either directly by setting {x:Null} or indirectly via a binding, a NullReferenceException is raised internally once the element is evaluated. This will then crash the application as it never handles the exception.

To Reproduce

Add this element to a View: <TextBlock Text="hello" FontFamily="{x:Null}"/>

You can also bind it from a ViewModel and setting it to null from there:

View: <TextBlock Text="hello" FontFamily="{Binding Field}"/>
ViewModel: public FontFamily? Field => null;

Expected behavior

No response

Avalonia version

11.0.10

OS

Windows

Additional context

No response

[timunie]

what is the use-case here?

[MB-GA]

what is the use-case here?

None in particular: we're migrating from WPF, and in the process of this we ran into this bug. I'm only really reporting it to raise awareness of it since it can be hard to track down the source, as the exception occurs internally in Avalonia. IMO it should at least give information of where you're passing null in the view so you can figure out where the mistake is made.

[Symbai]

@timunie This issue is already fixed. The PR author has just forgot to add this issue, instead he took his own issue number which was commented as a duplicate of this one: #15896