message: Created transitioner in constructor
  Only want to create the transitioner once when fragment first created. The transitioner for back navigation is recreated by the FragmentNavigator
diff: @@ -15,20 +15,18 @@ import java.util.HashSet;
  public class SceneFragment extends Fragment implements SharedElementContainer {
  private SceneView scene;
  - private HashSet<String> sharedElementNames;
  SceneFragment(SceneView scene, HashSet<String> sharedElements) {
  super();
  this.scene = scene;
  scene.fragment = this;
  - sharedElementNames = sharedElements;
  + if (sharedElements != null )
  + scene.transitioner = new SharedElementTransitioner(this, sharedElements);
  }
  @Nullable
  @Override
  public View onCreateView(@NonNull LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
  - if (sharedElementNames != null )
  - scene.transitioner = new SharedElementTransitioner(this, sharedElementNames);
  if (scene.transitioner != null)
  postponeEnterTransition();
  return scene;
  