public HiveIntervalYearMonth add(HiveIntervalYearMonth left, HiveIntervalYearMonth right) {
    HiveIntervalYearMonth result = null;
    if (left == null || right == null) {
      return null;
    }

    result = new HiveIntervalYearMonth(left.getTotalMonths() + right.getTotalMonths());
    return result;
  }
Perform date + int operation .
@param dt the date
@param interval the int (days)
@return the resulting date
ql/src/java/org/apache/hadoop/hive/ql/util/DateTimeMath.java