code: protected GuacamoleTunnel getTunnel(String tunnelUUID)
              throws GuacamoleException {
  
          // Pull tunnel from map
          GuacamoleTunnel tunnel = tunnels.get(tunnelUUID);
          if (tunnel == null)
              throw new GuacamoleResourceNotFoundException("No such tunnel.");
  
          return tunnel;
  
      }
docs: Returns the tunnel with the given UUID, if it has been registered with
  registerTunnel() and not yet deregistered with deregisterTunnel().
  
  @param tunnelUUID
  The UUID of registered tunnel.
  
  @return
  The tunnel corresponding to the given UUID.
  
  @throws GuacamoleException
  If the requested tunnel does not exist because it has not yet been
  registered or it has been deregistered.