Steps to Reproduce

1. Create a new Xamarin.Forms project targeting Android (used Xamarin.Forms 5.0.0.2196)
2. Execute the following statement: var t = Type.GetType(typeof(string).Name, (a) => null, null, false); at the beginning of the MainActivity.OnCreate method
3. Run the project

Current Behavior

Statement throws a NullReferenceException

Expected Behavior

No exception is thrown, and the call to Type.GetType returns null (this behavior is confirmed on .Net 4.7.2)

Stacktrace

Exception looks to be caused by a missing null check on asm in TypeSpec.cs

Contrast this with the dotnet/runtime version