public void discard() {
        context = null;
        callStack.clear();
        trace.clear();
    }
Discards this routable. Invoking this prevents the auto-generation of replies if you later discard the routable.
This is a required step to ensure safe shutdown if you need destroy a message bus instance while there are still
messages and replies alive in your application.
messagebus/src/main/java/com/yahoo/messagebus/Routable.java