code: void destroy() {
      destroyed = true;
  
      for (Map<String, ManagedObservable<?>> observableMap : groupMap.values()) {
        for (ManagedObservable<?> managedObservable : observableMap.values()) {
          managedObservable.cancel();
        }
        observableMap.clear();
      }
      groupMap.clear();
    }
docs: Cancels all subscriptions and releases references to Observables and Observers. No more
  Observables can be added to this group after it has been destroyed and it becomes unusable.