/**
     * Builds the OpenSearch query for popular words.
     * @return The QueryBuilder instance.
     */
    protected QueryBuilder buildQuery() {
        final BoolQueryBuilder queryBuilder = QueryBuilders.boolQuery();
        queryBuilder.must(QueryBuilders.termQuery(FieldNames.KINDS, SuggestItem.Kind.QUERY.toString()));
        queryBuilder.mustNot(QueryBuilders.existsQuery(FieldNames.READING_PREFIX + "1"));