private List<String> extractIds(SearchResponse response) {
   List<String> ids = new ArrayList<String>();
   for (SearchHit hit : response.getHits()) {
     if (hit != null) {
       ids.add(hit.getId());
     }
   }
   return ids;
 }
 private static String[] toArray(List<String> values) {
   String[] valuesAsArray = new String[values.size()];
   return values.toArray(valuesAsArray);
 }