use strict;
use warnings;

sub tst {
	warn "entering tst()\n";
	my $arg = shift;  # line 6
	warn "leaving tst()\n\n";
}

my %h=();
tst $h{''};
tst $h{undef};  # line 12
my $bla='';
tst $h{$bla};  # line 14
$bla=undef;
tst $h{$bla};  # line 16
undef $bla;
tst $h{$bla};  # line 19