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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 getSerializedResponse(self):
 """ Returns a string version of the SearchResponse that has been built by this SearchResponseBuilder. """

        self._protoObject.next_page_token = pb.string(self._nextPageToken)
        s = protocol.toJson(self._protoObject)
        return s