Notice: Undefined index when creating $cache_key

Hi,

when using the plugin I encountered notices which are generated by a missing check.

foreach ($params as $key) {
    if (isset($_GET[$key]))
	$args[$key] = urlencode($_GET[$key]);
    $cache_key .= ':' . $_GET[$key];
}

Can you move the $cache_key .= ':' . $_GET[$key]; within the if check to prevent the notice?

Thanks in advance ??

Kind regards,
Manuel