@Override
    public void handleMessage(Message msg) {
        if (destroyed.get()) {
            msg.discard();
            return;
        }
        if (msg.hasSequenceId()) {
            if (filter(msg)) {
                sequencedSend(msg);
            }
        } else {
            sender.handleMessage(msg); // unsequenced
        }
    }
All messages pass through this handler when being sent by the owning source session. In case the message has no
sequencing-id, it is simply passed through to the next handler in the chain. Sequenced messages are sent only if
there is no queue for their id, otherwise they are queued.

@param msg the message to send.
messagebus/src/main/java/com/yahoo/messagebus/Sequencer.java