I wanted to redefine the button order of the ButtonBar used in a DialogPane to be the order in which the ButtonTypes are added to the DialogPane. The documentation of ButtonBar.BUTTON_ORDER_NONE suggests, that this would do the trick, so I tried:

DialogPane dialogPane = new DialogPane() {
    @Override
    protected Node createButtonBar() {
        ButtonBar bar = (ButtonBar)super.createButtonBar();
        bar.setButtonOrder(ButtonBar.BUTTON_ORDER_NONE);
        return bar;
    }
};
dialogPane.getButtonTypes().add(ButtonType.FINISH);
dialogPane.getButtonTypes().add(ButtonType.CLOSE);
dialogPane.setContent(createContent());

This leads to an exception:
Exception in thread "JavaFX Application Thread" java.lang.IllegalStateException: ButtonBar buttonOrder string can not be null or empty
at com.sun.javafx.scene.control.skin.ButtonBarSkin.layoutButtons(ButtonBarSkin.java:142)
at com.sun.javafx.scene.control.skin.ButtonBarSkin.<init>(ButtonBarSkin.java:99)
at javafx.scene.control.ButtonBar.createDefaultSkin(ButtonBar.java:518)
...