If you use the system menubar in OS X with a MenuItem that has an ImageView set as the graphic but a null image then GlassSystemMenu throws a NullPointerException:

Exception in thread "JavaFX Application Thread" java.lang.NullPointerException
at com.sun.javafx.tk.quantum.GlassSystemMenu.getPixels(GlassSystemMenu.java:322)
at com.sun.javafx.tk.quantum.GlassSystemMenu.insertMenuItem(GlassSystemMenu.java:255)
at com.sun.javafx.tk.quantum.GlassSystemMenu.addMenuItem(GlassSystemMenu.java:198)
at com.sun.javafx.tk.quantum.GlassSystemMenu.insertMenu(GlassSystemMenu.java:165)
at com.sun.javafx.tk.quantum.GlassSystemMenu.addMenu(GlassSystemMenu.java:119)

You can see this issue if you run the following test 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.image.Image;
import javafx.scene.image.ImageView;
import javafx.scene.layout.BorderPane;
import javafx.stage.Stage;


public class MenuBarTest extends Application {

@Override public void start(final Stage primaryStage) throws Exception {

Menu menu = new Menu("File");
menu.getItems().add(new MenuItem("test", new ImageView((Image)null)));

MenuBar menuBar = new MenuBar();
menuBar.setUseSystemMenuBar(true);
menuBar.getMenus().add(menu);
BorderPane pane = new BorderPane();
pane.setTop(menuBar);
primaryStage.setScene( new Scene(pane, 400, 300) );
primaryStage.centerOnScreen();

primaryStage.show();

}

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

}