@Override
        boolean serialize(StringBuilder destination, BoolItem item) {
            destination.append(normalizeIndexName(item.getIndexName())).append(" = ");
            destination.append(item.stringValue());
            return false;
        }
Serialize Vespa query trees to YQL+ strings.

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