Match on undefined attribute.

[Matthew Schumacher]

List,

I can't seem to write a simple condition to match on a missing 
attribute.  I just want to do this:

                 if( ! &reply:Filter-Id ) {
                         update reply {
                                 Vendor-Address-List := foo
                         }
                 }


However, that always returns true, even if Filter-Id isn't returned in 
the Access-Accept.

If I try:
                 if( &reply:Filter-Id == "" ) {
                         update reply {
                                 Vendor-Address-List := foo
                         }
                 }

Then when Filter-Id isn't set, I get:

ERROR: Failed retrieving values required to evaluate condition

And no match.

What is the correct way to match on missing reply attributes?

Thanks,
schu