#!/usr/bin/perl

use strict;
use warnings FATAL => 'all';

while (reverse <DATA>) {
    warn defined($_) ? "defined\n" : "undefined\n";
    next unless defined($_);
    warn "$_\n";
}

exit 0;

__DATA__
this is line 1
this is line 2
this is line 3

##</code><code>##

undefined
Use of uninitialized value in reverse at text.pl line 6, <DATA> line 3.