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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_json(self):
 """ Convert to a json-serializable representation. Returns: dict: A dict representation that is json-serializable. """

        return {
            "xblock_id": six.text_type(self.xblock_id),
            "messages": [message.to_json() for message in self.messages],
            "empty": self.empty
        }