code: public DateTime plusHours(int hours) {
          if (hours == 0) {
              return this;
          }
          long instant = getChronology().hours().add(getMillis(), hours);
          return withMillis(instant);
      }
docs: Returns a copy of this datetime plus the specified number of hours.
  <p>
  The calculation will add a duration equivalent to the number of hours
  expressed in milliseconds.
  <p>
  For example, if a spring daylight savings cutover is from 01:59 to 03:00
  then adding one hour to 01:30 will result in 03:30. This is a duration
  of one hour later, even though the hour field value changed from 1 to 3.
  <p>
  The following three lines are identical in effect:
  <pre>
  DateTime added = dt.plusHours(6);
  DateTime added = dt.plus(Period.hours(6));
  DateTime added = dt.withFieldAdded(DurationFieldType.hours(), 6);
  </pre>
  <p>
  This datetime instance is immutable and unaffected by this method call.
  
  @param hours  the amount of hours to add, may be negative
  @return the new datetime plus the increased hours
  @since 1.1