code: private BigDecimal parseMediumNumber(final NumberBuffer buffer) {
          BigDecimal sum = BigDecimal.ZERO;
          BigDecimal result = parseMediumPair(buffer);
  
          if (result == null) {
              return null;
          }
  
          while (result != null) {
              sum = sum.add(result);
              result = parseMediumPair(buffer);
          }
  
          return sum;
      }
docs: Parses a "medium sized" number, typically less than 10,000（万）, but might be larger
  due to a larger factor from {link parseBasicNumber}.
  
  @param buffer buffer to parse
  @return parsed number, or null on error or end of input