code: private void handleException(final Throwable e)
      {
          if ( errorListeners.size() == 0 )
          {
              LOG.error("", e);
          }
          else
          {
              errorListeners.forEach(new Function<UnhandledErrorListener, Void>()
              {
                  @Override
                  public Void apply(UnhandledErrorListener listener)
                  {
                      try
                      {
                          listener.unhandledError("", e);
                      }
                      catch ( Exception e )
                      {
                          ThreadUtils.checkInterrupted(e);
                          LOG.error("Exception handling exception", e);
                      }
                      return null;
                  }
              });
          }
      }
docs: Send an exception to any listeners, or else log the error if there are none.