} catch (final ExecutionException e) {
            logger.warn("Failed to load popular words.", e);
        }
        return Collections.emptyList();
    }

    public void clearCache() {
        cache.invalidateAll();
    }

    protected String getCacheKey(final String seed, final String[] tags, final String[] roles, final String[] fields,
            final String[] excludes) {

        if (StringUtil.isBlank(pipeline)) {
            return OptionalThing.empty();
        }
        return OptionalThing.of(pipeline);
    }

    public void refresh() {
        crawlingConfigCache.invalidateAll();
    }

    public synchronized String store(final String sessionId, final CrawlingConfig crawlingConfig) {
        final String sessionCountId = sessionId + "-" + count;