code: public CompletableFuture<Void> destroy() {
          CompletableFuture<Void> ret;
          if (controllerProxy != null) {
              ret = controllerProxy.destroy();
              controllerProxy = null;
          } else {
              ret = new CompletableFuture<>();
              ret.complete(null);
          }
          return ret;
      }
docs: By calling this method the MVC group will be destroyed. This means that the controller instance on the server will
  be removed and the model that is managed and synchronized between client and server will be detached. After this method
  is called the view should not be used anymore. It's important to call this method to removePresentationModel all the unneeded references on
  the server.
  
  @return a future can be used to react on the destroy