CodeIgniter Like Flash Data in PHP

CodeIgniter

class FlashMessage {

    public static function render() {
        if (!isset($_SESSION['my_my_messages'])) {
            return null;
        }
        $my_messages = $_SESSION['my_messages'];
        unset($_SESSION['my_messages']);
        return implode('<br/>', $my_messages);
    }

    public static function add($message) {
        if (!isset($_SESSION['my_messages'])) {
            $_SESSION['my_messages'] = array();
        }
        $_SESSION['my_messages'][] = $message;
    }

}