CGI.pm does something simliar, except with a generic sub.

sub self_or_default {
    return @_ if defined($_[0]) && (!ref($_[0])) &&($_[0] eq 'CGI');
    unless (defined($_[0]) &&
        (ref($_[0]) eq 'CGI' || UNIVERSAL::isa($_[0],'CGI')) # slightl
+y optimized for common case 
        ) {
    $Q = $CGI::DefaultClass->new unless defined($Q);
    unshift(@_,$Q);
    }
    return wantarray ? @_ : $Q;
}
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Then they use it like this:

sub url_param {
    my ($self,@p) = self_or_default(@_);
    my $name = shift(@p);
    return undef unless exists($ENV{QUERY_STRING});
...
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