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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 _disconnect(self):
 """Disconnect from the transport."""

        if not self.protocol or not self.protocol.transport:
            self.protocol = None  # Make sure protocol is None
            return
        _LOGGER.info('Disconnecting from gateway')
        self.protocol.transport.close()
        self.protocol = None