public function setRoot(string $root = "F") : CNabuDataObject
    {
        if ($root === null) {
            throw new ENabuCoreException(
                    ENabuCoreException::ERROR_NULL_VALUE_NOT_ALLOWED_IN,
                    array("\$root")
            );
        }
        $this->setValue('nb_role_root', $root);
        
        return $this;
    }