code: public Period plusMinutes(int minutes) {
          if (minutes == 0) {
              return this;
          }
          int[] values = getValues();  // cloned
          getPeriodType().addIndexedField(this, PeriodType.MINUTE_INDEX, values, minutes);
          return new Period(values, getPeriodType());
      }
docs: Returns a new period plus the specified number of minutes added.
  <p>
  This period instance is immutable and unaffected by this method call.
  
  @param minutes  the amount of minutes to add, may be negative
  @return the new period plus the increased minutes
  @throws UnsupportedOperationException if the field is not supported