code: private function getOrCreateDefinition()
      {
          if ($this->container->hasDefinition(Contao2BackendViewDefinitionInterface::NAME)) {
              $view = $this->container->getDefinition(Contao2BackendViewDefinitionInterface::NAME);
              if (!$view instanceof Contao2BackendViewDefinitionInterface) {
                  throw new DcGeneralInvalidArgumentException(
                      'Configured BackendViewDefinition does not implement Contao2BackendViewDefinitionInterface.'
                  );
              }
              return $view;
          }
          $this->container->setDefinition(
              Contao2BackendViewDefinitionInterface::NAME,
              $view = new Contao2BackendViewDefinition()
          );
  
          return $view;
      }
docs: Get or create the definition.
  
  @return Contao2BackendViewDefinitionInterface
  
  @throws DcGeneralInvalidArgumentException When the contained view definition is of invalid type.