The th:if = ${object != null} is not rendering even though the condition is true

Question

Thymeleaf th:if object!= conditon not redering html.

My HTML template

    <th:block th:if="${user == null}">
      <li class="nav-item">
        <a class="nav-link" href="/signin">Login</a>
      </li>
    </th:block>

    <th:block th:if="${user != null}">
      <li class="nav-item">
        <a class="nav-link" href="/admin/user/register">Register</a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="/logout">Logout</a>
      </li>
    </th:block>

Controller code

@ModelAttribute
    public void getUserAndRole(Principal principal) {
        if (principal != null) {
            String name = principal.getName();
            User user = service.findByEmail(name) != null ? service.findByEmail(name) :   service.findByUsername(name);
            new ModelAndView().addObject("user", user);
        }
    }

    @GetMapping("/register")
    public ModelAndView register() {
        ModelAndView modelAndView = new ModelAndView("register");
        modelAndView.addObject("request", new UserRequest());
        return modelAndView;
    }

The navbar should be toggled depending on which condition is true.