use strict;
use warnings;
use 5.014;  

my @arr = ();

if (exists $arr[0]) {
    say 'yes';
}
else {
    say 'no';
}

say $arr[0];

--output:--
no
Use of uninitialized value in say at 1.pl line 15.

##</code><code>##

my @arr = (undef);

if (exists $arr[0]) {
    say 'yes';
}
else {
    say 'no';
}

say $arr[0];

--output:--
yes
Use of uninitialized value $arr[0] in say at 1.pl line 14.