After accessing a Menu by its mnemonic, pressing the left or the right arrow key will result in a NullPointerException.

Code:

import javafx.application.Application;
import javafx.scene.Scene;
import javafx.scene.control.Menu;
import javafx.scene.control.MenuBar;
import javafx.scene.control.MenuItem;
import javafx.scene.layout.StackPane;
import javafx.stage.Stage;

public class JavaFXApplication extends Application {

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

    @Override
    public void start(Stage primaryStage) {

        StackPane root = new StackPane();

        MenuBar menuBar = new MenuBar();
        Menu menuFile = new Menu("_File");
        MenuItem menuItem1 = new MenuItem("Foo");

        menuFile.getItems().add(menuItem1);
        menuBar.getMenus().add(menuFile);

        root.getChildren().add(menuBar);

        primaryStage.setScene(new Scene(root, 300, 250));
        primaryStage.show();
    }
}

Exception:
java.lang.NullPointerException
at com.sun.javafx.scene.control.skin.MenuBarSkin.isMenuEmpty(MenuBarSkin.java:728)
at com.sun.javafx.scene.control.skin.MenuBarSkin.showNextMenu(MenuBarSkin.java:781)
at com.sun.javafx.scene.control.skin.MenuBarSkin.access$600(MenuBarSkin.java:81)
at com.sun.javafx.scene.control.skin.MenuBarSkin$4.handle(MenuBarSkin.java:221)
at com.sun.javafx.scene.control.skin.MenuBarSkin$4.handle(MenuBarSkin.java:194)
at com.sun.javafx.scene.control.WeakEventHandler.handle(WeakEventHandler.java:62)
at com.sun.javafx.event.CompositeEventHandler.dispatchCapturingEvent(CompositeEventHandler.java:78)
at com.sun.javafx.event.EventHandlerManager.dispatchCapturingEvent(EventHandlerManager.java:202)
at com.sun.javafx.event.EventHandlerManager.dispatchCapturingEvent(EventHandlerManager.java:159)
at com.sun.javafx.event.CompositeEventDispatcher.dispatchCapturingEvent(CompositeEventDispatcher.java:22)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:31)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
at com.sun.javafx.event.BasicEventDispatcher.dispatchEvent(BasicEventDispatcher.java:35)
at com.sun.javafx.event.EventDispatchChainImpl.dispatchEvent(EventDispatchChainImpl.java:92)
at com.sun.javafx.event.EventUtil.fireEventImpl(EventUtil.java:53)
at com.sun.javafx.event.EventUtil.fireEvent(EventUtil.java:33)
at javafx.event.Event.fireEvent(Event.java:171)
at javafx.scene.Scene$KeyHandler.process(Scene.java:3509)
at javafx.scene.Scene$KeyHandler.access$2300(Scene.java:3468)
at javafx.scene.Scene.impl_processKeyEvent(Scene.java:1900)
at javafx.scene.Scene$ScenePeerListener.keyEvent(Scene.java:2266)
at com.sun.javafx.tk.quantum.GlassViewEventHandler.handleKeyEvent(GlassViewEventHandler.java:127)
at com.sun.glass.ui.View.handleKeyEvent(View.java:518)
at com.sun.glass.ui.View.notifyKey(View.java:951)
at com.sun.glass.ui.win.WinApplication._runLoop(Native Method)
at com.sun.glass.ui.win.WinApplication.access$100(WinApplication.java:29)
at com.sun.glass.ui.win.WinApplication$3$1.run(WinApplication.java:73)
at java.lang.Thread.run(Thread.java:722)