searchFieldSet = new HashSet<>();
            Collections.addAll(searchFieldSet, searchFields);
        }
        if (facetFields == null) {
            facetFields = fessConfig.getQueryAdditionalFacetFields(//
                    fessConfig.getIndexFieldUrl(), //
                    fessConfig.getIndexFieldHost(), //
                    fessConfig.getIndexFieldTitle(), //

        return list.toArray(new String[list.size()]);
    }

    String getQueryAdditionalFacetFields();

    default String[] getQueryAdditionalFacetFields(final String... fields) {
        final List<String> list = new ArrayList<>(fields.length + 10);
        stream(fields).of(stream -> stream.forEach(list::add));
        split(getQueryAdditionalFacetFields(), ",")

     * The value is, e.g.  <br>
     * comment: Additional facet fields for queries.
     * @return The value of found property. (NotNull: if not found, exception but basically no way)
     */
    String getQueryAdditionalFacetFields();

    /**
     * Get the value for the key 'query.additional.facet.fields' as {@link Integer}. <br>
     * The value is, e.g.  <br>
     * comment: Additional facet fields for queries.