I think this is a compiler bug.

The following console application compiles und executes flawlessly when compiled with VS 2015:

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            var x = MyStruct.Empty;
        }

        public struct MyStruct
        {
            public static readonly MyStruct Empty = new MyStruct();
        }
    }
}

But now it's getting weird: This code compiles, but it throws a TypeLoadException when executed.

namespace ConsoleApplication1
{
    class Program
    {
        static void Main(string[] args)
        {
            var x = MyStruct.Empty;
        }

        public struct MyStruct
        {
            public static readonly MyStruct? Empty = null;
        }
    }
}

Do you experience the same issue? If so, I will file an issue at Microsoft.

The code looks senseless, but I use it to improve readability and to achieve disambiguation.

I have methods with different overloads like

void DoSomething(MyStruct? arg1, string arg2)

void DoSomething(string arg1, string arg2)

Calling a method this way...

myInstance.DoSomething(null, "Hello world!")

... does not compile.

Calling

myInstance.DoSomething(default(MyStruct?), "Hello world!")

or

myInstance.DoSomething((MyStruct?)null, "Hello world!")

works, but looks ugly. I prefer it this way:

myInstance.DoSomething(MyStruct.Empty, "Hello world!")

If I put the Empty variable into another class, everything works okay:

public static class MyUtility
{
    public static readonly MyStruct? Empty = null;
}

Strange behavior, isn't it?

UPDATE 2016-03-29

I opened a ticket here: http://github.com/dotnet/roslyn/issues/10126

UPDATE 2016-04-06

A new ticket has been opened here: https://github.com/dotnet/coreclr/issues/4049