docs: def length(self):
          """
          Gives the length of the queue. Returns ``None`` if the queue is not
          connected.
  
          If the queue is not connected then it will raise
          :class:`retask.ConnectionError`.
  
          """
          if not self.connected:
              raise ConnectionError('Queue is not connected')
  
          try:
              length = self.rdb.llen(self._name)
          except redis.exceptions.ConnectionError as err:
              raise ConnectionError(str(err))
  
          return length