Delegates closed over null are broken in Mono

[MichalPetryka]

Description

Creating and calling a delegate closed over null in Mono leads to runtime errors due to invalid stubs being used, see godbolt for an example.

Reproduction Steps

using System;

internal class Program
{
    public static void Main()
    {
        Console.WriteLine(Nul());
    }

	public static bool Nul()
	{
		return new Func<bool>(new C().A).Method.CreateDelegate<Func<bool>>(null)();
	}

	internal class C
	{
		public bool A()
		{
			return this is null;
		}
	}
}

Expected behavior

Prints true.

Actual behavior

Unhandled Exception:
System.InvalidProgramException: Invalid IL code in (wrapper delegate-invoke) System.Func`1<bool>:invoke_callvirt_TResult (): IL_0066: ldarga.s  1


   at Program.Nul()
   at Program.Main()

Regression?

No idea.

Known Workarounds

Don't use Mono

Configuration

Mono main windows/linux x64

Other information

One issue I found was that Mono was incorrectly using target being null to decide the stub but even after I fixed that here, the issue was still broken.

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