docs: def union(self, streamSet):
          """
          Creates a stream that is a union of this stream and other streams
          
          Args:
              streamSet: a set of Stream objects to merge with this stream
          Returns:
              Stream:
          """
          if(not isinstance(streamSet,set)) :
              raise TypeError("The union operator parameter must be a set object")
          if(len(streamSet) == 0):
              return self        
          op = self.topology.graph.addOperator("$Union$")
          op.addInputPort(outputPort=self.oport)
          for stream in streamSet:
              op.addInputPort(outputPort=stream.oport)
          oport = op.addOutputPort(schema=self.oport.schema)
          return Stream(self.topology, oport)