code: def _get_handler_set(cls, request, fail_enum, header_proto=None):
          
          added = set()
          handlers = []
  
          for controls in request.sorting:
              control_bytes = controls.SerializeToString()
              if control_bytes not in added:
                  added.add(control_bytes)
                  handlers.append(
                      cls._ValueHandler(controls, fail_enum, header_proto))
  
          return handlers
docs: Goes through the list of ClientSortControls and returns a list of
          unique _ValueHandlers. Maintains order, but drops ClientSortControls
          that have already appeared to help prevent spamming.