in reply to
Hope a subroutine will return undef by default
What if instead of trying to bend Perl to be like ... well ... what language are you actually trying to mimic here? ... what if instead you just got used to Perl being Perl? I can understand a code policy requiring an explicit return statement ensured either by code review or (if such thing is possible) using Perl::Critic, but no matter what way you do it this is only ever gonna cause confusion and pain. I'm pretty sure you could do something using source code filters or somesuch hackery, but you really do not want to do that!
Enoch was right!
Enjoy the last years of Rome.