In DecodeableRpcResult:

```java
default:
                throw new IOException("Unknown result flag, expect '0' '1' '2', get " + flag);
```

But in fact, DecodeableRpcResult can recognize '3', '4', and '5'. 
throw new UnsupportedOperationException();
    }
    @Override
    public Object decode(Channel channel, InputStream input) throws IOException {
        ObjectInput in = CodecSupport.getSerialization(channel.getUrl(), serializationType)
                .deserialize(channel.getUrl(), input);
        byte flag = in.readByte();
        switch (flag) {
            case DubboCodec.RESPONSE_NULL_VALUE:
                break;
            case DubboCodec.RESPONSE_VALUE:
                handleValue(in);
                break;
            case DubboCodec.RESPONSE_WITH_EXCEPTION:
                handleException(in);
                break;
            case DubboCodec.RESPONSE_NULL_VALUE_WITH_ATTACHMENTS:
                handleAttachment(in);
                break;
            case DubboCodec.RESPONSE_VALUE_WITH_ATTACHMENTS:
                handleValue(in);
                handleAttachment(in);
                break;
            case DubboCodec.RESPONSE_WITH_EXCEPTION_WITH_ATTACHMENTS:
                handleException(in);
                handleAttachment(in);
                break;
            default:
                throw new IOException("Unknown result flag, expect '0' '1' '2', get " + flag);
        }