@Override
    public int getApproxSize() {
        if (buffer != null) {
            return buffer.getBuf().remaining();
        }
        return put.getDocument().getApproxSize();
    }
Returns the raw serialized buffer. This buffer is stored as the message is received from accross the network, and
deserialized from as soon as a member is requested. This method will return null if the buffer has been decoded.

@return the buffer containing the serialized data for this message, or null
documentapi/src/main/java/com/yahoo/documentapi/messagebus/protocol/PutDocumentMessage.java