docs: def zunionstore(self, dest, keys, aggregate=None):
          """
          Union multiple sorted sets specified by ``keys`` into
          a new sorted set, ``dest``. Scores in the destination will be
          aggregated based on the ``aggregate``, or SUM if none is provided.
          """
          with self.pipe as pipe:
              keys = [self.redis_key(k) for k in keys]
              return pipe.zunionstore(self.redis_key(dest), keys,
                                      aggregate=aggregate)