DB<132> use warnings; sub tst {my $a=shift, my $b =shift}

  DB<133> %h=()

  DB<134> $bla=""
 => ""

  DB<135> tst $h{$bla}
 => (undef, undef)

  DB<136> undef $bla
 => undef

  DB<137> tst $h{$bla}
Use of uninitialized value in scalar assignment at (eval 81)[multi_perl5db.pl:644] line 2.