code: public static <T> ChangeNotifier<T> aggregate(ChangeNotifier<T>... notifiers) {
      return aggregate(Arrays.asList(notifiers));
    }
docs: Creates a {@link ChangeNotifier} that aggregates the records provided by a list of notifiers.
  
  <p>A change event on any of the input notifiers will propagate up the the returned notifier.
  The set of previous and current records contained in the event will be the union of all
  records in the input notifiers, before and after the change event.
  
  @param notifiers  A list of notifiers to aggregate
  @param <T>        The record type
  @return A notifier with the described behaviour