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Solve the following problem using Python, implementing the functions described below, one line at a time
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Description:
 def to_pb(self):
 """Converts the union into a single GC rule as a protobuf. :rtype: :class:`.table_v2_pb2.GcRule` :returns: The converted current object. """

        union = table_v2_pb2.GcRule.Union(rules=[rule.to_pb() for rule in self.rules])
        return table_v2_pb2.GcRule(union=union)