function convertTimeZone($date, $to_tz, $from_tz = null) {
		throw new RuntimeException('Not implemented!');

		if ($to_tz instanceof DateTimeZone) {
			$to_tz = $to_tz->getName();
		}
		if ($from_tz instanceof DateTimeZone) {
			$from_tz = $from_tz->getName();
		}

		return "NEW_TIME($date, '$from_tz', '$to_tz')";
	}