// 0
Document doc = new Document();
addField(doc, groupField, "a", useDv);
addField(doc, "airport", "ams", useDv);
addField(doc, "duration", "5", useDv);
w.addDocument(doc);
// 1
doc = new Document();
addField(doc, groupField, "a", useDv);
addField(doc, "airport", "dus", useDv);