docs: @Override
      public boolean hasNext(int startPosition, int contentLength) {
          byte b = readByte();
          if (b == SIGN_HASNEXT) return true;
          if (b != SIGN_NONEXT) throw new ConvertException("hasNext option must be (" + (SIGN_HASNEXT)
                  + " or " + (SIGN_NONEXT) + ") but '" + b + "' at position(" + this.position + ")");
          return false;
      }