plperl function to return nulls

I can't find a reference in the docs for this...

I have a plperl function returning an int. The int is returned as the
result of a system call.

It is set to return a null if one of the inputs is null, but I can't see
how to return a null if the result is indeterminate. The function
currently returns a 0 instead.

How do I stick an if in the function to return a null where appropriate?


Thanks,

  Brent Wood