The situations where this would be needed are pretty contrived, IMHO. That would mean that someone is using hash keys of value zero or the empty string -- which is certainly allowable, but very contrived:

my %hash = (
    foo => 'bar',
    0   => 'baz',
    ''  => 'qux',
);

for (sort keys %hash) {
    next unless $_;
    print "$_ => $hash{$_}";
}

for (sort keys %hash) {
    print "$_ => $hash{$_}";
}
[download]

L-LL-L--L-LL-L--L-LL-L--
-R--R-RR-R--R-RR-R--R-RR
B--B--B--B--B--B--B--B--
H---H---H---H---H---H---
(the triplet paradiddle with high-hat)