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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):
 """ Serializes the event to JSON. :returns: a string """

        event_as_dict = copy.deepcopy(self.event_body)
        if self.timestamp:
            if "keen" in event_as_dict:
                event_as_dict["keen"]["timestamp"] = self.timestamp.isoformat()
            else:
                event_as_dict["keen"] = {"timestamp": self.timestamp.isoformat()}
        return json.dumps(event_as_dict)