docs: def is_alive(self):
          """Returns a flag with the state of the SSH connection."""
          null = chr(0)
          try:
              if self.device is None:
                  return {"is_alive": False}
              else:
                  # Try sending ASCII null byte to maintain the connection alive
                  self._send_command(null)
          except (socket.error, EOFError):
              # If unable to send, we can tell for sure that the connection is unusable,
              # hence return False.
              return {"is_alive": False}
          return {"is_alive": self.device.remote_conn.transport.is_active()}