Unable to find 'com/vaadin/DefaultWidgetSet.gwt.xml' on your classpath;

The same problem when using add-ons TouchKit , please help:

1. Create a project named mobile (refert to the attachment) and copy the code as the manual
@SuppressWarnings("serial")
@Theme("mobile")
@Title("My Mobile App")
public class MobileUI extends UI {

    @WebServlet(value = "/*", asyncSupported = true)
    @VaadinServletConfiguration(productionMode = false, ui = MobileUI.class)
    public static class Servlet extends VaadinServlet {
    }

    @Override
    protected void init(VaadinRequest request) {
        // Define a view
        class MyView extends NavigationView {
            public MyView() {
                super("Planet Details");

                CssLayout content = new CssLayout();
                setContent(content);

                VerticalComponentGroup group =
                        new VerticalComponentGroup();
                content.addComponent(group);

                group.addComponent(new TextField("Planet"));
                group.addComponent(new NumberField("Found"));
                group.addComponent(new Switch("Probed"));

                setRightComponent(new Button("OK"));
            }
        }

        // Use it as the content root
        setContent(new MyView());
    }

}

2. Add the setting of TouchKit in ivy
3. Add TouchKit  in MobileWidgetSet
<inherits name="com.vaadin.addon.touchkit.gwt.TouchKitWidgetSet" />

4. Compile WidgetSet
5. Launch and access the application
6. Report the following message
Widgetset 'com.vaadin.DefaultWidgetSet' does not contain implementation for null. Check its component connector's @Connect mapping, widgetsets GWT module description file and re-compile your widgetset. In case you have downloaded a vaadin add-on package, you might want to refer to add-on instructions.