MvvmCross9.0.2 throws System.NullReferenceException for Bind
## 🐛 Bug Report
System.NullReferenceException: "Object reference not set to an instance of an object."
 at MvvmCross.Binding.BindingContext.MvxBaseFluentBindingDescription`1.SourcePropertyPath[TSource](Expression`1 sourceProperty)\n   
at MvvmCross.Binding.BindingContext.MvxFluentBindingDescription`2.To(Expression`1 sourceProperty)

Note:MacOS App migrated from Xamarin.Mac to. NET6
<!--- Summary description of the bug --->

### Expected behavior
MacOS App starts up normally

### Reproduction steps
Create binding set and call bind.
![Screen Shot 2022-12-22 at 16 59 25](https://user-images.githubusercontent.com/121216002/209102417-2ebf94c4-0e84-4d80-b557-54df616050f9.png)

Sample Source Code：
[MvvmCross.NETSample.Mac.zip](https://github.com/MvvmCross/MvvmCross/files/10285670/MvvmCross.NETSample.Mac.zip)


### Configuration
・Visual Studio for Mac 17.5
・MvvmCross 9.0.2


**Platform:** 
- [ ] :iphone: iOS
- [ ] :robot: Android
- [ ] :checkered_flag: WPF
- [ ] :earth_americas: UWP
- [x] :apple: MacOS
- [ ] :tv: tvOS
- [ ] :monkey: Xamarin.Forms
