public static function set_404()
{
if (empty(URL::instance()->matched_rule) || URL::instance()->matched_rule->name != 'display_404') {
$rule = RewriteRules::by_name('display_404');
URL::instance()->matched_rule = reset($rule);
URL::instance()->matched_rule->match(self::$stub);
}
return URL::instance()->matched_rule;
}