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

    HiveIntervalDayTime result = new HiveIntervalDayTime();
    add(left, right, result);

    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