code: private BigDecimal parseMediumPair(final NumberBuffer buffer) {
  
          final BigDecimal first = parseBasicNumber(buffer);
          final BigDecimal second = parseMediumKanjiNumeral(buffer);
  
          if (first == null && second == null) {
              return null;
          }
  
          if (second == null) {
              // If there's no second factor, we return the first one
              // This can happen if we just have a plain number such as 五
              return first;
          }
  
          if (first == null) {
              // If there's no first factor, just return the second one,
              // which is the same as multiplying by 1, i.e. with 千
              return second;
          }
  
          // Return factors multiplied
          return first.multiply(second);
      }
docs: Parses a pair of "medium sized" numbers, i.e. large kanji factor is at most 1,000（千）
  
  @param buffer buffer to parse
  @return parsed pair, or null on error or end of input