Xamarin.Forms + NullGuard = crash at startup

[megafinz]

Hi.

I'm getting a crash at startup when I add NullGuard.Fody to my Xamarin.Forms project.

Steps to reproduce (using VS 2017 for Mac):

1. File -> New Solution -> Blank Forms App (C#) -> (doesn't matter if Shared Project / PCL or XAML / no XAML).
2. *.iOS -> Packages -> Add Packages -> NullGuard.Fody.
3. Add <NullGuard /> to FodyWeavers.xml.
4. Run the iOS app.
5. Crash (see below).

I'm using:

• Fody 2.1.2
• NullGuard.Fody 1.6.2
• Visual Studio Community 2017 for Mac (7.3 build 740)
• Xamarin.iOS 11.4.0.214
• Xamarin.Forms 2.4.0.280

Exception:

System.MethodAccessException: Method `System.Diagnostics.Private.Debug:Assert (bool,string)' is inaccessible from method `NullGuardTest.iOS.AppDelegate:FinishedLaunching (UIKit.UIApplication,Foundation.NSDictionary)'
  at at (wrapper managed-to-native) System.Object:__icall_wrapper_mono_throw_method_access (intptr,intptr)
  at NullGuardTest.iOS.AppDelegate.FinishedLaunching (UIKit.UIApplication app, Foundation.NSDictionary options) [0x00048] in /Users/megafinz/Projects/NullGuardTest/iOS/AppDelegate.cs:14
  at at (wrapper managed-to-native) UIKit.UIApplication:UIApplicationMain (int,string[],intptr,intptr)
  at UIKit.UIApplication.Main (System.String[] args, System.IntPtr principal, System.IntPtr delegate) [0x00005] in /Users/builder/data/lanes/5489/25c6ba1e/source/xamarin-macios/src/UIKit/UIApplication.cs:79
  at UIKit.UIApplication.Main (System.String[] args, System.String principalClassName, System.String delegateClassName) [0x00038] in /Users/builder/data/lanes/5489/25c6ba1e/source/xamarin-macios/src/UIKit/UIApplication.cs:63
  at NullGuardTest.iOS.Application.Main (System.String[] args) [0x00001] in /Users/megafinz/Projects/NullGuardTest/iOS/Main.cs:17

[tom-englert]

If "Debug.Assert" is not accessible in IOS, you can turn it off in configuration: IncludeDebugAssert="false"
see https://github.com/Fody/NullGuard#configuration

[megafinz]

Disabling Debug.Assert in configuration fixes the issue.

I tried using System.Diagnostics.Debug.Assert and it compiles and works fine, so Debug.Assert is in fact accessible. Exception message says that System.Diagnostics.**Private**.Debug.Assert is being used, maybe this is the source of the issue.