use 5.010;
use strict;
use warnings;

my $x = 42;
my $y;
my $z;

debug($x, $y);

say $z;

sub debug {
    no warnings 'uninitialized';
    say join ',', @_;
}

##</code><code>##

42,
Use of uninitialized value $z in say at szab.pl line 11.