docs: public static long parsePositiveLong(String str) {
          long value = 0;
          final int length = str.length();
  
          if (length == 0) {
              throw new NumberFormatException(str);
          }
  
          long multiplier = 1;
          for (int i = length - 1; i >= 0; --i) {
              char c = str.charAt(i);
  
              if (c < '0' || c > '9') {
                  throw new NumberFormatException(str);
              }
              long digit = c - '0';
              value += digit * multiplier;
              multiplier *= 10;
          }
          return value;
      }