docs: @NonNull
      private Transition getTransition(@NonNull Scene scene) {
          Transition transition;
          ViewGroup sceneRoot = scene.getSceneRoot();
          // TODO: cached in Scene instead? long-term, cache in View itself
          Scene currScene = Scene.getCurrentScene(sceneRoot);
          if (currScene != null) {
              ArrayMap<Scene, Transition> sceneTransitionMap = mScenePairTransitions.get(scene);
              if (sceneTransitionMap != null) {
                  transition = sceneTransitionMap.get(currScene);
                  if (transition != null) {
                      return transition;
                  }
              }
          }
          transition = mSceneTransitions.get(scene);
          return (transition != null) ? transition : sDefaultTransition;
      }