public function triggerHook($params=NULL) {
		if( !isset($params) ) {
			$params = array(
				0 => null,
			);
		} else if( !is_array($params) ) {
			$params = array(
				0 => $params,
			); 
		}
		foreach($this->callbacks as $callback) {
			$r	= call_user_func_array($callback, $params);
			if( $r !== NULL ) {
				$params[0] = $r;
			}
		}
		return isset($params[0]) ? $params[0] : null;
	}