like === of JS

sub eqq {
    my ($s1, $s2) = @_;

    if (! defined $s1) {
        return ! defined $s2;
    }
    elsif (! defined $s2) {
        return '';
    }

    if (ref $s1 ne ref $s2) { return ''; }

    return $s1 eq $s2;
}