public void add(final DurationAdder durationAdder) {
        Objects.requireNonNull(durationAdder);
        this.secondsAdder.add(durationAdder.secondsAdder.sum());
        this.nanosAdder.add(durationAdder.nanosAdder.sum());
    }
Add durationAdder's duration to the current duration.

@return The duration after adding durationAdder
stroom-util/src/main/java/stroom/util/concurrent/DurationAdder.java