* @param threshold The threshold date.
     * @return The SuggestDeleteResponse.
     */
    public SuggestDeleteResponse deleteOldWords(final ZonedDateTime threshold) {
        ensureOperations();
        return deletionOps.deleteOldWords(index, threshold);
    }

    /**
     * Sets the index name.
     * @param index The index name.
     * @return This SuggestIndexer instance.
     */

     *
     * @param index The index name
     * @param threshold The threshold date
     * @return The SuggestDeleteResponse
     */
    public SuggestDeleteResponse deleteOldWords(final String index, final ZonedDateTime threshold) {
        if (logger.isInfoEnabled()) {
            logger.info("Deleting old words: index={}, threshold={}", index, threshold);
        }

        suggester.refresh();

        long totalWordsCount = suggester.getAllWordsNum();
        assertTrue(totalWordsCount > oldWordsCount);

        SuggestDeleteResponse deleteResponse = suggester.indexer().deleteOldWords(threshold);

        assertNotNull(deleteResponse);
        assertFalse(deleteResponse.hasError());

        suggester.refresh();
        long remainingWordsCount = suggester.getAllWordsNum();

        SuggestResponse response3 = suggester.suggest().setQuery("検索").setSuggestDetail(true).execute().getResponse();
        assertEquals(1, response3.getNum());

        suggester.indexer().deleteOldWords(threshold);
        suggester.refresh();

        SuggestResponse response4 = suggester.suggest().setQuery("柿").setSuggestDetail(true).execute().getResponse();
        assertEquals(0, response4.getNum());