I've got a function that I want passed a reference when it is called. (It's a reference to an instance of a custom script.) But I'm thinking I'd like an option to call this function without sending this reference. Normally to have an optional variable I just supply a default value. But since I'm using a reference, wouldn't that mean I'd have to create a new instance the use as the default value? That sounds like creating garbage. What I would want is just to be able to pass a null reference, and then my function can check for a null reference. But how do I do that? How can I pass a null reference to this function, or create a null reference as its default value?