public static <T extends IIdentifyable>List<T> checkIds(@NonNull List<T> items){
  for (int i=0, size=items.size(); i < size; i++) {
    checkId(items.get(i));
  }
  return items;
}

public static < T extends IIdentifyable > List < T > checkIds ( @ NonNull List < T > items ) { for ( int i = 0 , size = items . size ( ) ; i < size ; i ++ ) { checkId ( items . get ( i ) ) ; } return items ; }
set an unique identifier for all items which do not have one set already
