code: protected void deregisterTunnel(GuacamoleTunnel tunnel) {
          tunnels.remove(tunnel.getUUID().toString());
          logger.debug("Deregistered tunnel \"{}\".", tunnel.getUUID());
      }
docs: Deregisters the given tunnel such that future read/write requests to
  that tunnel will be rejected.
  
  @param tunnel
  The tunnel to deregister.