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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 builds(self):
 """ Access the builds :returns: twilio.rest.serverless.v1.service.build.BuildList :rtype: twilio.rest.serverless.v1.service.build.BuildList """

        if self._builds is None:
            self._builds = BuildList(self._version, service_sid=self._solution['sid'], )
        return self._builds