protected ByteBuf internalBuffer() {
        if (cumulation != null) {
            return cumulation;
        } else {
            return Unpooled.EMPTY_BUFFER;
        }
    }
Returns the internal cumulative buffer of this decoder. You usually
do not need to access the internal buffer directly to write a decoder.
Use it only when you must use it at your own risk.
src/main/java/com/alipay/remoting/codec/AbstractBatchDecoder.java