@Override
        public void onExit() {
            SerializerWrapper w = state.removeFirst();
            w.type.onExit(destination, w.item);
            w = state.peekFirst();
            if (w != null) {
                w.subItems += 1;
            }
        }
Serialize Vespa query trees to YQL+ strings.

@author Steinar Knutsen
container-search/src/main/java/com/yahoo/search/yql/VespaSerializer.java