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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 close_link(self):
 """Close the communication link."""

        logger.info('Closing link')
        if (self.link is not None):
            self.commander.send_setpoint(0, 0, 0, 0)
        if (self.link is not None):
            self.link.close()
            self.link = None
        self._answer_patterns = {}
        self.disconnected.call(self.link_uri)