}
        final Set<RequestData> urlSet = new HashSet<>(docList.size());
        for (final Map<String, Object> doc : docList) {
            final String url = DocumentUtil.getValue(doc, fessConfig.getIndexFieldUrl(), String.class);
            if (StringUtil.isNotBlank(url)) {
                urlSet.add(RequestDataBuilder.newRequestData().get().url(url).build());
            }
        }