code: private String getKey(String key) throws IllegalArgumentException {
      String checkKey =
          JobHistoryKeys.HADOOP2_TO_HADOOP1_MAPPING.containsKey(key) ? JobHistoryKeys.HADOOP2_TO_HADOOP1_MAPPING
              .get(key) : key;
      return (JobHistoryKeys.valueOf(checkKey).toString());
    }
docs: maintains compatibility between hadoop 1.0 keys and hadoop 2.0 keys. It also confirms that this
  key exists in JobHistoryKeys enum
  @throws IllegalArgumentException NullPointerException