In both NSTextFieldCell and NSTextField the property TextColor should allow null value.
According to the documentation those fields are of type NSColor?

https://developer.apple.com/documentation/appkit/nstextfield/1399409-textcolor
https://developer.apple.com/documentation/appkit/nstextfieldcell/1447151-textcolor

Steps to Reproduce

1. Create an instance of NSTextField
2. Set TextColor to some random color
3. Set TextColor back to default system color by assigning it's value to null

Expected Behavior

No exception is thrown.

Actual Behavior

System.ArgumentNullException is thrown
Parameter name: value at ObjCRuntime.ThrowHelper.ThrowArgumentNullException (System.String argumentName) [0x00001] in /Library/Frameworks/Xamarin.Mac.framework/Versions/9.1.0.5/src/Xamarin.Mac/ObjCRuntime/ThrowHelper.cs:28 at ObjCRuntime.NativeObjectExtensions.GetNonNullHandle (ObjCRuntime.INativeObject self, System.String argumentName) [0x00009] in /Library/Frameworks/Xamarin.Mac.framework/Versions/9.1.0.5/src/Xamarin.Mac/ObjCRuntime/INativeObject.cs:33 at AppKit.NSTextField.set_TextColor (AppKit.NSColor value) [0x00007] in /Library/Frameworks/Xamarin.Mac.framework/Versions/9.1.0.5/src/Xamarin.Mac/AppKit/NSTextField.g.cs:1006

Environment

Xamarin iOS & Mac 16.2.0.5

Build Logs

Example Project (If Possible)