public Date add(Date dt, HiveIntervalYearMonth interval) {
    if (dt == null || interval == null) {
      return null;
    }

    Date dtResult = new Date();
    add(dt, interval, dtResult);

    return dtResult;
  }
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