title: Xamarin - ios xaml Preview fail with monotouch error
body: <p>I am experimenting a fail on xaml preview on my Xamarin project on VisualStudio for MAC 7.6.4.
  After some update, xaml no render yet the preview showing a System.NullReferenceaException as showed in the picture.</p>
  
  <p>Any help about tht issue?
  <a href="https://i.stack.imgur.com/OR5Fo.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/OR5Fo.png" alt="enter image description here"></a></p>