http://www.perlmonks.org?node_id=678155


in reply to cleaning up in DESTROY

FWIW, I've seen undef being passed as first parameter to DESTROY in earlier 5.8.x versions of Perl when using threads and at global destruction. I would consider that as a bug, but it *does* seem to happen (in fact, some of my Thread:: modules with DESTROY methods explicitely check for that eventuality). Liz