Multiple Scenes on Nez.FNA

Program.cs

// YOU NEED MY MULTISCENE BRANCH: https://github.com/Alan-FGR/Nez/tree/multiscene

class TestScene : MScene
{
    public override void initialize()
    {
        base.initialize();
        setDesignResolution(640,360,SceneResolutionPolicy.ShowAll);
        renderer = new DefaultRenderer();
        renderer.renderTexture = new RenderTexture(640,360);
        addRenderer(renderer);
        Physics.gravity = Vector2.Zero;
        var p = createEntity("player");
        p.addComponent(new PlayerController());
        p.position = Vector2.One * 150;
    }
}

class TestUIScene : MScene, IFinalRenderDelegate
{
    public override void initialize()
    {
        base.initialize();
        setDesignResolution(640,360,SceneResolutionPolicy.ShowAll);
        renderer = new DefaultRenderer();
        renderer.renderTexture = new RenderTexture(640,360);
        addRenderer(renderer);
        var canvas = createEntity("ui").addComponent(new UICanvas());
        var skin = Skin.createDefaultSkin();
        var table = canvas.stage.addElement(new Window("window", skin)).setMovable(true).setResizable(true);
        table.pad(10).setPosition(10, 10);
        table.padTop(30);
        var button = new TextButton("click", skin);
        table.add(button).size(100,20).setRow();
        table.pack();

        finalRenderDelegate = this;
    }

    public Scene scene { get; set; }
    public void onAddedToScene(){}
    public void onSceneBackBufferSizeChanged(int newWidth, int newHeight){}

    public void handleFinalRender(Color letterboxColor, RenderTarget2D source, Rectangle finalRenderDestinationRect, SamplerState samplerState)
    {
        renderer.render(scene);
        Core.graphicsDevice.setRenderTarget( null );
        Graphics.instance.batcher.begin( BlendState.Opaque, samplerState, null, null );
        Graphics.instance.batcher.draw( TestGame.gameScene_.renderer.renderTexture, finalRenderDestinationRect );
        Graphics.instance.batcher.end();
        Graphics.instance.batcher.begin( BlendState.AlphaBlend, samplerState, DepthStencilState.None, RasterizerState.CullNone, null );
        Graphics.instance.batcher.draw( renderer.renderTexture, finalRenderDestinationRect );
        Graphics.instance.batcher.end();
    }
}

public class MScene : Scene
{
    public Renderer renderer;
}

class TestGame : Core
{
    public static MScene gameScene_;
    protected override void Initialize()
    {
        base.Initialize();
        Window.AllowUserResizing = true;
        debugRenderEnabled = true;
        Screen.setSize(1281,721);
        Transform.shouldRoundPosition = false;

        gameScene_ = new TestScene();
        gameScene_.begin();

        var UIscene = new TestUIScene();
        UIscene.begin();

        scenes.Add(gameScene_);
        scenes.Add(UIscene);
    }
}

class Program
{
    private static TestGame game;
    static void Main(string[] args)
    {
        game = new TestGame();
        game.Run();
    }
}