code: async def sunionstore(self, dest, keys, *args):
          
          res = await self.sunion(keys, *args)
          await self.delete(dest)
  
          return await self.sadd(dest, *res)
docs: Store the union of sets specified by ``keys`` into a new
          set named ``dest``.  Returns the number of keys in the new set.
  
          Cluster impl:
              Use sunion() --> Dlete dest key --> store result in dest key
  
              Operation is no longer atomic.