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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 fields(self):
 """ Access the fields :returns: twilio.rest.autopilot.v1.assistant.task.field.FieldList :rtype: twilio.rest.autopilot.v1.assistant.task.field.FieldList """

        if self._fields is None:
            self._fields = FieldList(
                self._version,
                assistant_sid=self._solution['assistant_sid'],
                task_sid=self._solution['sid'],
            )
        return self._fields