❔ `delegate*` wrapper throws `System.BadImageFormatException`

using Microsoft.FSharp.Core;

public unsafe struct FuncPtr<TArg, TRet>
{
    private readonly nint ptr;

    public FuncPtr(nint ptr) => this.ptr = ptr;

    public TRet Call(TArg arg)
    {
        if (typeof(TRet) == typeof(Unit))
        {
            if (typeof(TArg) == typeof(Unit))
                ((delegate* unmanaged<void>)ptr)();
            else
                ((delegate* unmanaged<TArg, void>)ptr)(arg);

            return default!;
        }
        else
        {
            return typeof(TArg) == typeof(Unit) ? 
                ((delegate* unmanaged<TRet>)ptr)() : 
                ((delegate* unmanaged<TArg, TRet>)ptr)(arg);
        }
    }
}

using KiDev.IlAsm.FuncPtr;
using Microsoft.FSharp.Core;
using System.Runtime.InteropServices;

unsafe
{
    delegate* unmanaged<int> x = &Test;
    Console.WriteLine($"delegate* = {x()}"); // fine 

    var ptr = new FuncPtr<Unit, int>((nint)x);
    Console.WriteLine($"FuncPtr = {ptr.Call(null!)}"); // exception
}

[UnmanagedCallersOnly]
static int Test() => 12;