code: protected int[] mergePeriodInto(int[] values, ReadablePeriod period) {
          for (int i = 0, isize = period.size(); i < isize; i++) {
              DurationFieldType type = period.getFieldType(i);
              int value = period.getValue(i);
              checkAndUpdate(type, values, value);
          }
          return values;
      }
docs: Merges the fields from another period.
  
  @param values  the array of values to update
  @param period  the period to add from, not null
  @return the updated values
  @throws IllegalArgumentException if an unsupported field's value is non-zero