return !validateDateTimeString(source.get(s));
                }).collect(Collectors.toList()));
    }

    default boolean validateDateTimeString(final Object obj) {
        if (FessFunctions.parseDate(obj.toString()) != null) {
            return true;
        }
        return false;
    }

    String getIndexAdminIntegerFields();

    default Set<String> getIndexAdminIntegerFieldSet() {

     */
    protected Date parseLastModifiedDate(final String value) {
        // Try Apache DateUtils first (handles standard HTTP date formats)
        final Date date = DateUtils.parseDate(value);
        if (date != null) {
            return date;
        }
        // Fallback to custom pattern for non-standard formats (e.g., single-digit day)
        try {