Differentiate between zero (float) and null (or 0 int)

Is there any way to tell the difference between zero (float) and null, or at least 0 (int) and 0.0 (float)? I want to determine if an expression exists for an object. If I do a getexpression() for an expression that doesn't exist (say x in a container), it returns 0 (int), if it does exist then I get a float. If that float is 0.0, how can I tell if the expression is null or just has a value of 0.0? In lemur, null == 0 == 0.0.

Thanks,
A

Hmm
Interesting, must admit that nothing pops of the top of my head for this one . . .
Will have to give it a bit of thought, I think this may have come up once before but not resolved . . .
Have to get back to you . . .
Cheers
MM