use feature qw( say );
my @a;
{ say open(my $fh, '<', $a[0]) ? 1 : 0; }  # 1
$a[1] = undef;
{ say open(my $fh, '<', $a[0]) ? 1 : 0; }  # 1
$a[0] = undef;
{ say open(my $fh, '<', $a[0]) ? 1 : 0; }  # 0
delete($a[0]);
{ say open(my $fh, '<', $a[0]) ? 1 : 0; }  # 1