code: public function getForm($key, $asInstance = true)
      {
          $form = parent::getForm($key, $asInstance);
          
          /*
           * We must check here, if a lazy loaded top level form is an
           * instance of Container.
           */
          if ($asInstance && false === strpos($key, '.') && (!$form instanceof Container || !$form->getLabel())) {
              throw new \UnexpectedValueException(sprintf(
                                                      'The registered form with key "%s" is not an instance of \Core\Form\Container or does not have a label.',
                                                      $key
                                                  ));
          }
  
          return $form;
      }
docs: Gets a specific formular.
  
  This formular will be created upon the first retrievement.
  If created, the formular gets passed the formular parameters set in this container.
  
  @see Container::getForm
  
  @param string $key
  @param bool   $asInstance if false, the specification array is returned.
  
  @return Container|null|\Zend\Form\FormInterface|array
  @throws \UnexpectedValueException