docs: public static long getVisibilityCacheTimeout(FluoConfiguration conf, TimeUnit tu) {
      long millis = conf.getLong(VISIBILITY_CACHE_TIMEOUT, VISIBILITY_CACHE_TIMEOUT_DEFAULT);
      if (millis <= 0) {
        throw new IllegalArgumentException("Timeout must positive for " + VISIBILITY_CACHE_TIMEOUT);
      }
      return tu.convert(millis, TimeUnit.MILLISECONDS);
    }