code: @Override
      public void onClientConnectionError(final Object client, final SynchronizeFXException e) {
          serverCallback.onClientConnectionError(client, e);
      }
docs: Logs the unexpected disconnection of an client.
  
  Connection errors to single clients are usually non fatal. The server can still work correctly for the other
  clients. Because of that this type of error is just logged here and not passed to the user.
  
  @param client An object that represent the client where the error occurred.
  @param e an exception that describes the problem.
  @see NetworkToTopologyCallbackServer#onClientConnectionError(SynchronizeFXException)