private static class TestFessConfig extends FessConfig.SimpleImpl {
        private static final long serialVersionUID = 1L;

        @Override
        public String getApiPingSearchEngineFields() {

    }

    String getApiPingSearchEngineFields();

    default Set<String> getApiPingEsFieldSet() {
        Set<String> value = (Set<String>) propMap.get(API_PING_SEARCH_ENGINE_FIELD_SET);
        if (value == null) {
            value = split(getApiPingSearchEngineFields(), ",")

     * comment: Fields for API ping to search engine.
     * @return The value of found property. (NotNull: if not found, exception but basically no way)
     */
    String getApiPingSearchEngineFields();

    /**
     * Get the value for the key 'virtual.host.headers'. <br>
     * The value is, e.g.  <br>
     * comment: Virtual Host: Host:fess.codelibs.org=fess