anchor.diff:  ///  * null: nil
   ///  * [bool]\: `NSNumber numberWithBool:`
   ///  * [int]\: `NSNumber numberWithInt:` for values that are representable using
  -///    32-bit two's complement; otherwise, `NSNumber numberWithLong:` for values
  -///    that are representable using 64-bit two's complement; otherwise,
  -///    `FlutterStandardBigInteger`.
  +///    32-bit two's complement; `NSNumber numberWithLong:` otherwise
   ///  * [double]\: `NSNumber numberWithDouble:`
   ///  * [String]\: `NSString`
   ///  * [Uint8List], [Int32List], [Int64List], [Float64List]\:
  
positive.code:       throw const FormatException('Invalid method call');
    }
  
  
    @override
    ByteData encodeSuccessEnvelope(dynamic result) {
      final WriteBuffer buffer = new WriteBuffer();
  
negative.code:         result = buffer.getInt64();
          break;
        case _kLargeInt:
          // Flutter Engine APIs to use large ints have been deprecated on
          // 2018-01-09 and will be made unavailable.
          // TODO(mravn): remove this case once the APIs are unavailable.
          final int length = _readSize(buffer);
          final String hex = UTF8.decoder.convert(buffer.getUint8List(length));
          result = int.parse(hex, radix: 16);
  