private void appendKeyValue(StringBuilder destination, PredicateQueryItem.EntryBase entry) {
            destination.append('"');
            escape(entry.getKey(), destination);
            destination.append("\":");
            if (entry instanceof PredicateQueryItem.Entry) {
                destination.append('"');
                escape(((PredicateQueryItem.Entry) entry).getValue(), destination);
                destination.append('"');
            } else {
                destination.append(((PredicateQueryItem.RangeEntry) entry).getValue());
                destination.append('L');
            }
        }
Serialize Vespa query trees to YQL+ strings.

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