code: protected String cleanAppId(String appId) {
      return (appId != null) ? StringUtil.cleanseToken(appId) : Constants.UNKNOWN;
    }
docs: Given a potential value for appId, return a string that is safe to use in
  the jobKey
  
  @param appId
  possibly null value.
  @return non-null value stripped of separators that are used in the jobKey.