protected function getParentMultiRepoDir()
    {
        $rootConfig = $this->config->get('root_extra_config');
        if (!empty($rootConfig[self::KEY_MULTI_REPO_PARENT_DIR])) {
            $rootConfig[self::KEY_MULTI_REPO_PARENT_DIR] = rtrim($rootConfig[self::KEY_MULTI_REPO_PARENT_DIR], '\\/');
            if ($this->io->isVeryVerbose()) {
                $this->io->write('    Multi-repository path will be in custom parent directory.');
            }
            return $rootConfig[self::KEY_MULTI_REPO_PARENT_DIR];
        }
        if (!isset($rootConfig[self::KEY_MULTI_REPO_IN_CACHE]) || $rootConfig[self::KEY_MULTI_REPO_IN_CACHE]) {
            if ($this->io->isVeryVerbose()) {
                $this->io->write('    Multi-repository path will be in "cache-repo-dir".');
            }
            return $this->config->get('cache-repo-dir');
        }
        return null;
    }