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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 on_get(self, request, response, user_id=None):
 """Responds to GET request for users."""

        response.body = "{}"
        if self.handler(user_id):
            response.status = falcon.HTTP_200
            self.api.register(utils.mxid2localpart(user_id))
        else:
            response.status = falcon.HTTP_404