private void notifyTransmit() {
        List<RoutingNode> sendTo = new ArrayList<>();
        Deque<RoutingNode> stack = new ArrayDeque<>();
        stack.push(this);
        while (!stack.isEmpty()) {
            RoutingNode node = stack.pop();
            if (node.isActive) {
                if (node.children.isEmpty()) {
                    if (node.reply != null) {
                        node.notifyParent();
                    } else {
                        sendTo.add(node);
                    }
                } else {
                    for (RoutingNode child : node.children) {
                        stack.push(child);
                    }
                }
            }
        }
        if (!sendTo.isEmpty()) {
            net.send(msg, sendTo);
        }
    }
This method collects all unsent leaf nodes and passes them to {@link Network#send(com.yahoo.messagebus.Message,
java.util.List)}. This is orthogonal to {@link #notifyAbort(String)} in that it ensures that a reply will return
to sender.
messagebus/src/main/java/com/yahoo/messagebus/routing/RoutingNode.java