code: @NonNull
      public Bundle saveInstanceState() {
          Bundle bundle = new Bundle();
  
          bundle.putBundle(KEY_VIEW_CONTROLLER_BUNDLE, controller.saveInstanceState());
  
          if (pushControllerChangeHandler != null) {
              bundle.putBundle(KEY_PUSH_TRANSITION, pushControllerChangeHandler.toBundle());
          }
          if (popControllerChangeHandler != null) {
              bundle.putBundle(KEY_POP_TRANSITION, popControllerChangeHandler.toBundle());
          }
  
          bundle.putString(KEY_TAG, tag);
          bundle.putInt(KEY_INDEX, transactionIndex);
          bundle.putBoolean(KEY_ATTACHED_TO_ROUTER, attachedToRouter);
  
          return bundle;
      }
docs: Used to serialize this transaction into a Bundle