private function beautifyAuthorList($authors)
    {
        if ($authors === null) {
            return null;
        }

        $authors = \array_intersect_key($authors, \array_unique(\array_map('strtolower', $authors)));
        \usort($authors, 'strcasecmp');

        $mapped = [];
        foreach ($authors as $author) {
            $mapped[\strtolower($author)] = $author;
        }

        return $mapped;
    }