Hello Renato,
The function postmodern:connected-p should fail when its argument is a variable bounded to nil?
Yes, I think it should. It is defined on connection objects, nothing else. Having it take NIL might be convenient, but that kind of tricks are the road to (*shrudder*) a Perl-like mess of shortcuts and bizarre rules. Just use (AND *DATABASE* (CONNECTED-P *DATABASE*)) in your code.
Regards, Marijn