public function deleteContentTypeGroup($contentTypeGroupId)
    {
        $contentTypeGroup = $this->contentTypeService->loadContentTypeGroup($contentTypeGroupId);

        $contentTypes = $this->contentTypeService->loadContentTypes($contentTypeGroup);
        if (!empty($contentTypes)) {
            throw new ForbiddenException('Only empty content type groups can be deleted');
        }

        $this->contentTypeService->deleteContentTypeGroup($contentTypeGroup);

        return new Values\NoContent();
    }