The sequence number of this command. This is the sequence
        number assigned by the issuing client.

def sequence_number(self):
        """
        The sequence number of this command. This is the sequence
        number assigned by the issuing client.
        """
        entry = self._proto.commandQueueEntry
        if entry.cmdId.HasField('sequenceNumber'):
            return entry.cmdId.sequenceNumber
        return None