Redirect on spring boot

I wrote login system on spring-boot but there is a problem when I want to login, spring take login and password from form but cannot redirect to the account page.

Controller

Error

 @PostMapping(value = "user/login")
public String login(Model model, HttpSession session, @RequestParam("login") String login, @RequestParam("password") String password) {
    try {
        User user = userService.checkLogin(login, password);
        if (user == null) {
            model.addAttribute("err", "Login Valid login and password");
            return "/login";
        } else {
            if (user.getRole().equals(userService.Role_Admin)) {
                userService.addUserInSession(user, session);

                return "/admin/account";
            } else if (user.getRole().equals(userService.Role_Student)) {
                userService.addUserInSession(user, session);
                return "/student/account";
            } else {
                model.addAttribute("err", "Invalid User Role");
                return "/login";
            }
        } } catch (UserException ex) {
        model.addAttribute("err", ex.getMessage());
        return "/login";
    }

}