I think you probably don't want to create a new CGI object every time you call the sub. It would be expensive and there's no need. The call style ( @_, '' ) is kinda weird too and would fail under strict as written. Here's a redraft.

use CGI (); # at top of script/module

# transparently take over function param() if desired
sub param {
    my $param = shift || return;
    my @values = CGI::param($param);
    return '' unless @values;
    return wantarray ? @values : $values[0];
}
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