public function commit(array $mutations, array $options = [])
    {
        $options += [
            'transaction' => null
        ];

        $res = $this->connection->commit($options + [
            'mode' => ($options['transaction']) ? 'TRANSACTIONAL' : 'NON_TRANSACTIONAL',
            'mutations' => $mutations,
            'projectId' => $this->projectId
        ]);

        return $res;
    }