docs: boolean addIndexedField(ReadablePeriod period, int index, int[] values, int valueToAdd) {
          if (valueToAdd == 0) {
              return false;
          }
          int realIndex = iIndices[index];
          if (realIndex == -1) {
              throw new UnsupportedOperationException("Field is not supported");
          }
          values[realIndex] = FieldUtils.safeAdd(values[realIndex], valueToAdd);
          return true;
      }