code: public function handle(BuildWidgetEvent $event)
      {
          if (!$this->wantToHandle($event) || ($event->getProperty()->getName() !== 'filterparams')) {
              return;
          }
  
          $model = $event->getModel();
  
          $objFilterSettings  = $this->settingFactory->createCollection($model->getProperty('filter'));
          $extra              = $event->getProperty()->getExtra();
          $extra['subfields'] = $objFilterSettings->getParameterDCA();
          $event->getProperty()->setExtra($extra);
      }
docs: Build the filter params for the widget.
  
  @param BuildWidgetEvent $event The event.
  
  @return void