Optional String parameter?

[RickJ]

How do I make a String parameter optional as shown below?   

// Module Script
struct WinBlu  {
   // Some stuff
   // :

   import static String   Data(String Name, String Value=null);

   // Some more stuff
   // :
};

When I set it equal to null or to ""  I get the error below.  If I set it to zero
the compiler is happy but I don't think that is right either.   

Error (line xxx): Parameter default value must be literal

I assume I am missing something really obvious here;  it makes me feel so damm noobish.     

[Pumaman]

You can only have optional parameters for int and float parameters.

[RickJ]

Whew, I feel way better now.    Thanks ...

[monkey0506]

CJ you are no fun.  You can set it to 0 to make it optional (as you already figured out) and then in the function just pretend as if it's null...it works in any case.  You know me...I'm not big on "conventional."

[RickJ]

Generally speaking null is not necessarily guaranteed to be equal to 0 for all situations for all time.  If it were, there  wouldn't need to be a keyword for it. 

[monkey0506]

Well actually I think the keyword is just something of a simplification.  Kind of like the enumerated bool value "false".  It's equal to 0 and unless some major failure of logic takes place in the near future, it always will be.

I understand the concern about using 0 instead of null and whatever...but...

I'm not big on "conventional.

[EDIT:]

Oh...and I think it's worthy of mentioning that enumerated values (including bool) are handled internally as an integral type, so they can be optional as well.