docs: def is_alive(self):
          """Returns a flag with the state of the connection."""
          null = chr(0)
          if self.device is None:
              return {"is_alive": False}
          if self.transport == "telnet":
              try:
                  # Try sending IAC + NOP (IAC is telnet way of sending command
                  # IAC = Interpret as Command (it comes before the NOP)
                  self.device.write_channel(telnetlib.IAC + telnetlib.NOP)
                  return {"is_alive": True}
              except UnicodeDecodeError:
                  # Netmiko logging bug (remove after Netmiko >= 1.4.3)
                  return {"is_alive": True}
              except AttributeError:
                  return {"is_alive": False}
          else:
              # SSH
              try:
                  # Try sending ASCII null byte to maintain the connection alive
                  self.device.write_channel(null)
                  return {"is_alive": self.device.remote_conn.transport.is_active()}
              except (socket.error, EOFError):
                  # If unable to send, we can tell for sure that the connection is unusable
                  return {"is_alive": False}
          return {"is_alive": False}