code: def to_pb(self):
          
          union = table_v2_pb2.GcRule.Union(rules=[rule.to_pb() for rule in self.rules])
          return table_v2_pb2.GcRule(union=union)
docs: Converts the union into a single GC rule as a protobuf.
  
          :rtype: :class:`.table_v2_pb2.GcRule`
          :returns: The converted current object.