NullPointerException in MenuButton

I get a NPE, when I try to set the graphic of a MenuButton in the ActionEvent of one of the MenuItems.

java.lang.NullPointerException
at com.sun.javafx.scene.control.skin.LabeledImpl$1.invalidated(Unknown Source)
at com.sun.javafx.binding.ExpressionHelper$SingleInvalidation.fireValueChangedEvent(Unknown Source)
at com.sun.javafx.binding.ExpressionHelper.fireValueChangedEvent(Unknown Source)
at javafx.beans.property.ObjectPropertyBase.fireValueChangedEvent(Unknown Source)
at javafx.beans.property.ObjectPropertyBase.markInvalid(Unknown Source)
at javafx.beans.property.ObjectPropertyBase.set(Unknown Source)
at javafx.beans.property.ObjectProperty.setValue(Unknown Source)
at javafx.scene.control.Labeled.setGraphic(Unknown Source)


Run the code, click the MenuButton, and then the MenuItem.

import javafx.application.Application;
import javafx.event.ActionEvent;
import javafx.event.EventHandler;
import javafx.scene.Scene;
import javafx.scene.control.Label;
import javafx.scene.control.MenuButton;
import javafx.scene.control.MenuItem;
import javafx.scene.layout.VBox;
import javafx.stage.Stage;

public class TestApp3 extends Application {


    public static void main(String[] args) throws Exception {
        launch();
    }

    public void start(final Stage stage) throws Exception {


        VBox root = new VBox();

        final MenuButton button = new MenuButton("Click me");

        MenuItem item = new MenuItem("Click me");
        item.setOnAction(new EventHandler<ActionEvent>() {
            @Override
            public void handle(ActionEvent actionEvent) {
                button.setGraphic(new Label("Test")); // THIS CAUSES NPE !
            }
        });

        button.getItems().add(item);

        root.getChildren().add(button);

        Scene scene = new Scene(root);
        stage.setScene(scene);
        stage.show();
    }
}