* comment: Index name for crawler documents.
     * @return The value of found property. (NotNull: if not found, exception but basically no way)
     */
    String getIndexDocumentCrawlerIndex();

    /**
     * Get the value for the key 'index.document.crawler.queue.number_of_shards'. <br>
     * The value is, e.g. 10 <br>
     * comment: Number of primary shards for crawler queue index.

                    .indices()
                    .prepareDelete(//
                            fessConfig.getIndexDocumentCrawlerIndex() + ".queue", //
                            fessConfig.getIndexDocumentCrawlerIndex() + ".data", //
                            fessConfig.getIndexDocumentCrawlerIndex() + ".filter")
                    .execute(ActionListener.wrap(res -> {