Thymeleaf报错：找不到bean名称'emp'的请求属性问题求助

最近在开发Thymeleaf项目，已经实现员工列表展示、部门选择以及员工删除功能，现在要实现向指定部门添加员工的功能，但遇到了超出预期的问题。我尝试创建新的Employee对象并加入模型，再通过输入框录入员工信息，但emp对象似乎缺失，具体错误信息如下：

Caused by: java.lang.IllegalStateException: Neither BindingResult nor plain target object for bean name 'emp' available as request attribute

我的Controller类代码：

@Controller
@Slf4j
@SessionAttributes({"department"})
@RequestMapping("/department")
public class DepartmentController {

    @Autowired
    private DepartmentRepository departmentRepository;

    @Autowired
    private EmployeeRepository employeeRepository;

    @PostConstruct
    public void initDB(){

        Path path = Paths.get(System.getProperty("user.dir"), "src", "main", "resources", "data.json");
        ObjectMapper mapper = new ObjectMapper().registerModule(new JavaTimeModule());
        List<Department> departments = null;

        try {

            departments = mapper.readValue(path.toFile(), new TypeReference<List<Department>>() {});

            if(departments != null){

                for(Department department : departments){

                    department.getEmployees().forEach(e -> e.setDepartment(department));

                }

                departmentRepository.saveAll(departments);

            }

        } catch (IOException e) {
            throw new RuntimeException(e);
        }

    }

    @GetMapping
    public String getDepartments(Model model){

        List<Department> departments = departmentRepository.findAll();
        model.addAttribute("depts", departments);

        return "departmentView";

    }

    @PostMapping
    public String getEmployeesOfDepartment(Model model, @RequestParam("deptName") String departmentName){

        Department department = departmentRepository.getDepartmentByDeptNo(departmentName);

        updateModel(model, department);
        return "departmentView";

    }

    @PostMapping("/remove/{empId}")
    public String removeEmployeeFromDepartment(Model model, @SessionAttribute("department") Department department, @PathVariable("empId") Integer empId) {

        Employee employee = employeeRepository.findByEmployeeNo(empId);
        department.getEmployees().remove(employee);
        employeeRepository.delete(employee);
        departmentRepository.flush();

        updateModel(model, department);
        return "departmentView";
    }

    @PostMapping("/create")
    public String addEmployee(Model model, @SessionAttribute("department") Department department, @ModelAttribute("emp") Employee employee){

        department.addEmployee(employee);
        employee.setDepartment(department);
        employeeRepository.save(employee);

        updateModel(model, department);
        return "departmentView";

    }

    public void updateModel(Model model, Department department){

        model.addAttribute("depts", departmentRepository.findAll());
        model.addAttribute("department", department);
        model.addAttribute("selectedDepartment", department.getDeptName());
        model.addAttribute("manager", department.getDeptManager());
        model.addAttribute("emp", new Employee());
        model.addAttribute("employees", department.getEmployees());

    }

}

我的department模板代码：

<!DOCTYPE html>
<html lang="en" xmlns:th="https://www.thymeleaf.org">
<head>
    <meta charset="UTF-8">
    <title>Departments</title>
</head>
<body>

<h1>Department</h1>

<form method="post" th:action="@{/department}">

    <label for="choice"></label>
    <select id="choice" name="deptName" onchange="submit();">
        <option th:each="department : ${depts}" th:value="${department.deptNo}" th:text="${department.deptName}" th:selected="${department.deptName == selectedDepartment}"></option>
    </select>

</form>

<table>
    <form method="post">

        <tr th:if="${manager != null}">
            <td th:value="${manager.employeeNo}" th:text="${manager.employeeNo}"></td>
            <td th:value="${manager.firstName}" th:text="${manager.firstName}"></td>
            <td th:value="${manager.lastName}" th:text="${manager.lastName}"></td>
            <td th:value="${manager.gender}" th:text="${manager.gender}"></td>
        </tr>

    </form>

    <form method="post" th:each="employee : ${employees}">

        <tr>
            <td th:value="${employee.employeeNo}" th:text="${employee.employeeNo}"></td>
            <td th:value="${employee.firstName}" th:text="${employee.firstName}"></td>
            <td th:value="${employee.lastName}" th:text="${employee.lastName}"></td>
            <td th:value="${employee.gender}" th:text="${employee.gender}"></td>
            <td>
                <form method="post">
                    <input type="submit" value="Remove" th:formaction="@{/department/remove/{empId}(empId=${employee.employeeNo})}">
                </form>
            </td>
        </tr>

    </form>

</table>

<form method="get">
    <button>Add Employee</button>
</form>

<form method="post" th:action="@{/department/create}" th:object="${emp}">

    <label th:for="employeeNo">Employee Number: </label>
    <input type="text" th:field="*{employeeNo}">
    <br>
    <label th:for="firstname">First Name: </label>
    <input th:field="*{firstname}" type="text">
    <br>
    <label th:for="lastname">Last Name: </label>
    <input th:field="*{lastname}" type="text">
    <br>
    <label th:for="gender">Gender: </label>
    <input th:field="*{gender}" type="text">
    <br>
    <button onclick="submit();">Add Employee</button>

</form>

</body>
</html>

我已经试过YouTube教程、Baeldung文章、Thymeleaf官方文档，甚至咨询过ChatGPT，但问题仍未解决，希望能得到帮助。

内容的提问来源于stack exchange，提问作者Gahatma