I typically initialize variables explicitly to undef (as in my $var = undef;) if I cannot produce a meaningful initial value at that point in the program. If this is done, then the test to later determine if a value was produced is simply defined($var) and usually producing an undefined value is just as bad as producing no value, so die "..." unless defined($var); works well to bail out on error later.

And just a reminder, you are including use strict; and use warnings;, right?