private function createRootFolders(OutputInterface $output)
    {
        $em = $this->container->get('doctrine.orm.default_entity_manager');
        $repository = $this->container->get('ekyna_media.folder.repository');

        $name = FolderInterface::ROOT;
        $output->write(sprintf(
            '- <comment>%s</comment> %s ',
            ucfirst($name),
            str_pad('.', 44 - mb_strlen($name), '.', STR_PAD_LEFT)
        ));

        if (null !== $folder = $repository->findRoot()) {
            $output->writeln('already exists.');
        } else {
            $folder = new Folder();
            $folder->setName($name);

            $em->persist($folder);
            $em->flush();

            $output->writeln('created.');
        }
    }