public Timestamp add(Timestamp ts, HiveIntervalYearMonth interval) {
    if (ts == null || interval == null) {
      return null;
    }

    Timestamp tsResult = new Timestamp();
    add(ts, interval, tsResult);

    return tsResult;
  }
Perform month arithmetic to millis value using UTC time zone.
@param millis
@param months
@return
ql/src/java/org/apache/hadoop/hive/ql/util/DateTimeMath.java