*
     * @return a string containing the execution result with the number of deleted files or error message
     */
    public String execute() {
        try {
            final long count = ComponentUtil.getThumbnailManager().purge(getExpiry());
            return "Deleted " + count + " thumbnail files.";
        } catch (final Exception e) {
            logger.error("Failed to purge thumbnails.", e);
            return e.getMessage();

            }
            return newDoc;
        }).toList();
        if (fessConfig.isThumbnailCrawlerEnabled()) {
            final ThumbnailManager thumbnailManager = ComponentUtil.getThumbnailManager();
            final String thumbnailField = fessConfig.getIndexFieldThumbnail();
            docList.stream().forEach(doc -> {
                if (!thumbnailManager.offer(doc)) {