public function get($archiverId, $isAvailable = null)
    {
        $this->has($archiverId, true);

        if ($isAvailable === null) {
            return $this->archivers[$archiverId];
        }

        if ($this->archivers[$archiverId]->isAvailable() === (bool) $isAvailable) {
            return $this->archivers[$archiverId];
        }

        return null;
    }