final private function checkScalarValue(string $scalar):bool
    {
        if ($this->strlikeInArray($scalar, $this->scalar) !== false) {
            return (true);
        } else {
            throw new Server500(new \ArrayObject(array("explain" => "Unknow type $scalar in Mercure",
                "solution" => "Type must be : ".json_encode($this->scalar))));
        }
    }