A DESCRIPTION OF THE PROBLEM :
I want to get owner node of ContextMenu (call `ContextMenu.getOwnerNode`) but the result is null, like this:
```
public class App extends Application {
    @Override
    public void start(Stage primaryStage) throws Exception {
        MenuItem menuItem = new MenuItem("Click me");
        menuItem.setOnAction(event -> {
            String text = menuItem.getParentPopup().getOwnerNode() != null ? "Owner node is not null" : "Owner node is null";
            new Alert(Alert.AlertType.INFORMATION, text).showAndWait();
        });

        ContextMenu contextMenu = new ContextMenu(menuItem);

        Button button = new Button("Right click me");
        button.setContextMenu(contextMenu);

        primaryStage.setScene(new Scene(new BorderPane(button)));
        primaryStage.show();
    }
}
```

Set breakpoint in `ContextMenu.doShow`, `anchor` parameter is not null. The reason is that when ContextMenu is set to Control (call `Control.setContextMenu`), `ContextMenu.isShowRelativeToWindow` is true, it only set `ownerWindow` and not set `ownerNode`.