// 8
doc = new Document();
addField(doc, groupField, "a", useDv);
addField(doc, "airport", "bru", useDv);
addField(doc, "duration", "10", useDv);
w.addDocument(doc);
indexSearcher.getIndexReader().close();
indexSearcher = newSearcher(w.getReader());
groupedAirportFacetCollector = createRandomCollector(useDv ? "hotel_dv" : "hotel", useDv ? "airport_dv" : "airport", null, !useDv);
indexSearcher.search(new MatchAllDocsQuery(), groupedAirportFacetCollector);