[Omaha.pm] uppercasing some things in complex nested structures

This isn't recursive or general use or anything, but it's what I came up with to uppercase specific things in 16 different use cases in some software I'm working on today... I thought it was pretty clean given the task at hand. Feedback welcome. :)

sub uppercase_everything {
   my ($self, $qualifiers) = @_;
   foreach my $key (keys %$qualifiers) {
      # these two have to remain lower case or OWS pukes
      next if ($key =~ /^(primary|preferred)$/);
      if (ref($qualifiers->{$key}) eq "ARRAY") {
         # Ack. Sometimes an arrayref is handed in.
         for (@{$qualifiers->{$key}}) {
            if (ref $_ eq "HASH") {
               # Ack. Hashref inside the arrayref (e.g. UserDefinedValues)
               my $href = "">               foreach my $key (keys %$href) {
                  $href->{$key} = uc $href->{$key};
               }
            } else {
               # Simple scalars in our arrayref (e.g. AddressLine)
               next unless (defined $_);
               tr/a-z/A-Z/;
            }
         }
      } elsif (ref($qualifiers->{$key}) eq "HASH") {
         # Are we supposed to uppercase any hashrefs?
      } else {
         # Simple scalar
         $qualifiers->{$key} = uc $qualifiers->{$key};
      }
   }
   #warn Dumper($qualifiers);
   return 1;
}

# Test uppercase_everything().
# 'lower' values should stay lowercase. 'upper's should turn to 'UPPER'
my $in = {
   primary   => 'lower',
   test1     => 'upper',
   preferred => 'lower',
   test2     => [ 'upper', 'upper'],
   test3     => [ { test4 => 'upper', test5 => 'upper' } ]
};
ok($c->uppercase_everything($in),       'uppercase_everything()');
is($in->{primary},             'lower', 'primary');
is($in->{test1},               'UPPER', 'test1');
is($in->{preferred},           'lower', 'preferred');
is($in->{test2}->[0],          'UPPER', 'test2');
is($in->{test2}->[1],          'UPPER', 'test2');
is($in->{test3}->[0]->{test4}, 'UPPER', 'test4');
is($in->{test3}->[0]->{test5}, 'UPPER', 'test5');