docs: @Override
      public void handleAbout(ApplicationEvent ae) {
          if (mainApp != null) {
              ae.setHandled(true);
              // We need to invoke modal About Dialog asynchronously
              // otherwise the Application queue is locked for the duration
              // of the about Dialog, which results in a deadlock if a URL is
              // selected, and we get a ReOpenApplication event when user
              // switches back to Findbugs.
              javax.swing.SwingUtilities.invokeLater(() -> mainApp.about());
          } else {
              throw new IllegalStateException("handleAbout: " + "MyApp instance detached from listener");
          }
      }