How to Passs NULL as a IDispatch Pointer to method?

[Yingpu Zhao]

Thanks to Larry.
I want to pass the IDispatch pointer of other COM object to
AddShapeInfo or pass null to tell x do nothing.
for example.

Rect= Dispatch("Rect.Document")
ShapeSet = Dispatch("xxx.Document")
ShapeSet.AddShapeInfo("Rect", 0, Shape)

or

ShapeSet.AddShapeInfo("EmptyShape", 0, None)