Thread: passing nullable type to a P/invoked function

Does anyone know of a way I can pass a nullable type to a p/invoked function? specifically I need parameter 1 of:

Code:

[DllImport("setupapi.dll", CharSet = CharSet.Auto, SetLastError = true)]
    static extern IntPtr SetupDiGetClassDevs(ref Guid ClassGuid, int? enumerator, IntPtr hwndParent, uint Flags);

to be passable so I can avoid have to overload the function.