#!/usr/bin/perl -w
use strict;
use Data::Dumper;

use constant index1 => 0;
use constant index2 => 1;

my $rec = [ undef, 1 ];
print Dumper($rec);                       # inspect before if

print "$rec->[index1] $rec->[index2]\n";  # warnings here (line 11)

if ( defined $rec->[index1] &&
     $rec->[index1] ne '' &&
     defined $rec->[index1] &&
     $rec->[index1] eq '1' )
{
    print "OK\n";
} else {
    print "Not OK\n";
}

print Dumper($rec);     # and check again after if

##</code><code>##

$VAR1 = [
          undef,
          1
        ];
Use of uninitialized value at ./p09.pl line 11.
 1
Not OK
$VAR1 = [
          undef,
          1
        ];