public void setReply(Reply reply) {
        if (reply != null) {
            shouldRetry = resender != null && resender.shouldRetry(reply);
            trace.getRoot().addChild(reply.getTrace().getRoot());
            reply.getTrace().clear();
        }
        this.reply = reply;
    }
Sets the reply of this routing node. This method also updates the internal state of this node; it is tagged for
resending if the reply has only transient errors, and the reply's {@link Trace} is copied. This method <u>does
not</u> call the parent node's {@link #notifyMerge()}.

@param reply The reply to set.
messagebus/src/main/java/com/yahoo/messagebus/routing/RoutingNode.java