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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 nack(self, channel_id=None, **kwargs):
 # pragma: no cover """Send a negative read-acknowledgement to the service. Causes the channel's read point to move to its previous position prior to the last poll. Args: channel_id (str):
 The channel ID. **kwargs: Supported :meth:`~pancloud.httpclient.HTTPClient.request` parameters. Returns: requests.Response: Requests Response() object. Examples: Refer to ``event_nack.py`` example. """

        path = "/event-service/v1/channels/{}/nack".format(channel_id)
        r = self._httpclient.request(
            method="POST",
            url=self.url,
            path=path,
            **kwargs
        )
        return r