public void discard() {
        if (handler != null) {
            handler.handleReply(null);
        } else if (parent != null) {
            parent.discard();
        }
    }
Discards this routing node. Invoking this will notify the parent {@link SendProxy} to ensure that the
corresponding message is discarded. This is a required step to ensure safe shutdown if you need to destroy a
message bus instance while there are still routing nodes alive in your application.
messagebus/src/main/java/com/yahoo/messagebus/routing/RoutingNode.java