* @param q The query string.
     * @param fields The fields to search in.
     * @return The QueryBuilder instance.
     */
    protected QueryBuilder buildQuery(final String q, final List<String> fields) {
        try {
            final QueryBuilder queryBuilder;
            if (Strings.isNullOrEmpty(q)) {
                queryBuilder = QueryBuilders.matchAllQuery();
            } else {