You can get this with the simple program like the following:

perl -we '$SIG{__DIE__} = undef'
[download]

Basically you aren't allowed to assign undef values to %SIG slots. Instead you need something like:

$SIG{__DIE__} = defined $origHandler ? origHandler : 'DEFAULT'
[download]

Although arguably Perl ought to be smart enough to DWIM. I might fix this.

Dave.