NavbarDropDownButton displaying blank links

Question

I'm trying to use Wicket-Bootstrap Navbar and NavbarDropDownButton inside my Wicket Application to display a list of links.

Web application is built with Wicket 8.7.0 and Wicket-Boostrap-core 3.0.0-M13.

The component I added to the Wicket Panel seems to work correctly, but once I click on the main link to display the dropdown content, all links are blank. Anyway I can click the links and they made their job. Here's the picture taken from the browser:

Here's the HTML used:

        ....
        <div class="navbar" wicket:id="utenteNavbar">
    </div>
</div>

while this is my Java code:

        Model<String> cambioPasswordStringModel = Model.of(getString("cambioPassword"));

    Navbar navbar = new Navbar("utenteNavbar");
    INavbarComponent dropDownComponent = new INavbarComponent() {

        @Override
        public ComponentPosition getPosition() {
            return Navbar.ComponentPosition.LEFT;
        }

        @Override
        public Component create(String markupId) {
            NavbarDropDownButton dropdownButton = new NavbarDropDownButton(Model.of(welcomeMessage)) {

                @Override
                protected List<AbstractLink> newSubMenuButtons(String buttonMarkupId) {
                    final List<AbstractLink> linksList = new ArrayList<AbstractLink>();
                    AjaxLink<String> cambioPasswordLink = new AjaxLink<String>(buttonMarkupId,
                            cambioPasswordStringModel) {

                        @Override
                        public void onClick(AjaxRequestTarget target) {
                            setResponsePage(CambioPasswordPage.class);
                        }
                    };

                    linksList.add(cambioPasswordLink);
                    return linksList;
                }
            };
            return dropdownButton;
        }
    };
    navbar.addComponents(dropDownComponent);
    add(navbar);

    add(welcomeMessageLabel);

Where's the mistake? Maybe I'm missing something on the CSS side?

Hope everything is clear, thanks for any help.