While certainly being convertible to IBinding x:Null shouldn't be treated as one

src/Markup/Avalonia.Markup.Xaml/XamlIl/CompilerExtensions/Transformers/AvaloniaXamlIlBindingPropertyAssignmentsTransformer.cs

@@ -18,6 +18,8 @@ namespace Avalonia.Markup.Xaml.XamlIl.CompilerExtensions.Transformers
                 var types = context.GetAvaloniaTypes();
                 
                 var vn = pv.Values[0];
+                if (vn.Type.GetClrType().Equals(XamlIlPseudoType.Null))
+                    return node;
                 
                 // Special handling for markup extensions
                 if (vn.Type.IsMarkupExtension)