html格式

<form th:object="${klient}" th:action="@{/osoba}" method="post">
                        <div class="form-row">
                            <div class="form-group col-md-4">
                                <label >Imię</label>
                                <input type="text" class="form-control"  th:field="*{imie}" >
                            </div>

                            <div class="form-group col-md-4">
                                <label >Nazwisko</label>
                                <input type="text" class="form-control" th:field="*{nazwisko}" >
                            </div>
                                <div class="select-list" id="selectlist">
                                    <select th:field="*{UserId}" >
                                        <option> -- </option>
                                        <option  th:each=" users : ${user}"
                                                 th:value="${users.UserId}"
                                                 th:utext="${users.lastName}"/>
                                    </select>
                                </div>

鳕鱼

@RequestMapping (value = "/osoba", method = RequestMethod.POST)
public String dodaj (Klient klient){
    System.out.print(klient);
    return "redirect:/osoba";
}
@RequestMapping (value = "/dodaj" , method = RequestMethod.GET)
public String tworz (Model model){
    model.addAttribute("klient" , new Klient());

    List<User> lista = userService.getAllUser();
    model.addAttribute("user" , lista);

    return "dodaj";
}

我想创建一个窗体，让他在其中完成客户端的字段并为他分配一个现有用户。问题是我无法获取所选的用户id。
我收到一条关于第一个选择的信息
执行处理器“org.thymeleaf.spring5.processor.springselectfieldtagprocessor”时出错