WellCommerce\Component\Form\Event\FormEvent::getFormBuilder PHP Method

    public function getFormBuilder() : FormBuilderInterface
    {
        return $this->formBuilder;
    }

 /**
  * Adds theme configuration fields to main theme edit form
  *
  * @param FormEvent $event
  */
 public function onThemeFormInit(FormEvent $event)
 {
     $builder = $event->getFormBuilder();
     $resource = $event->getEntity();
     $fieldGenerator = $this->container->get('theme.fields_generator');
     $fieldGenerator->loadThemeFieldsConfiguration($resource);
     $fieldGenerator->addFormFields($builder);
 }