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

        $res = $this->connection->commit($this->arrayFilterRemoveNull([
            'mutations' => $mutations,
            'session' => $session->name(),
            'database' => $session->info()['database']
        ]) + $options);

        $time = $this->parseTimeString($res['commitTimestamp']);
        return new Timestamp($time[0], $time[1]);
    }