open currently returns an Undef PMC if it fails to open a file. Should it instead return a None? Or, IMO, a Null?
Someone should probably do a cleanup in the core on None vs. Undef vs. Null to insure they are used consistently and appropriately. FWIW, it also seems unfair (or at least, unobvious) that there is are C<isnull> and C<null> opcodes, but no corresponding codes for Undef or None.
