@Override
        @SuppressWarnings("removal") // TODO Vespa 9: remove
        public void process(Message msg) {
            if (route != null) {
                msg.setRoute(route);
            }
            msg.setTimeRemaining(getTimeRemaining());
            msg.setRetryEnabled(retryEnabled);
            msg.getTrace().setLevel(Math.max(getFeederOptions().getTraceLevel(), traceLevel));

            if (priority != null) {
                ((DocumentMessage) msg).setPriority(priority);
            }
        }
Explicit priority set. May be null
vespaclient-core/src/main/java/com/yahoo/feedapi/MessagePropertyProcessor.java