Spring Boot和Thymeleaf错误：无法解析异常

Question

我正在使用Spring Boot，Spring Data，Thymeleaf创建一个TO-DO列表。任何人都可以告诉我，我的语法是否正确。这是我第一次使用spring boot的应用程序。我收到此错误org.thymeleaf.exceptions.TemplateProcessingException: Could not parse as expression: "" (index)

这是index.html

<div th:if test="${mode=='MODE_HOME'}">
        <div class="container" id ="homeDiv">
            <div class="jumbotron text-center">
                <h1>Welcome to Tasks Manager</h1>
            </div>
        </div>
    </div>

    <div th:if test="${mode=='MODE_TASKS'}">
        <div class="container text-center" id ="tasksDiv">
            <h3>My Tasks</h3>
            <hr/>
            <div class="table-responsive">
                <table class="table table-striped table-bordered text-left">
                    <thead>
                    <tr>
                        <th>ID</th>
                        <th>Name</th>
                        <th>Description</th>
                        <th>Date</th>
                        <th>Finished</th>
                    </tr>
                    </thead>
                    <tbody>
                    <tr th:each="task: ${tasks}">
                        <td th:text="${task.id}"></td>
                        <td th:text="${task.name}"></td>
                        <td th:text="${task.description}"></td>
                        <td th:text="${task.dateCreated}"></td>
                        <td th:text="${task.finished}"></td>
                    </tr>
                    </tbody>
                </table>
            </div>
        </div>

    </div>

    <div th:if test="${mode=='MODE_NEW' || mode=='MODE_UPDATE'}">
        <div class="container text-center">
            <h3>Manage Task</h3>
            <hr/>
            <form class="form-horizontal" method="POST" action="save-task">
                <input type="hidden" name="id" value="${task.id}"/>
                <div class="form-group">
                    <label class="control-label col-md-3">Name</label>
                    <div class="col-md-7">
                        <input type="text" class="form-control" name="name"  placeholder="name" value="${task.name}"/>
                    </div>

                </div>

                <div class="form-group">
                    <label class="control-label col-md-3">Description</label>
                    <div class="col-md-7">
                        <input type="text" class="form-control" name="description"  placeholder="name" value="${task.description}"/>
                    </div>

                </div>

                <div class="form-group">
                    <label class="control-label col-md-3">Finished</label>
                    <div class="col-md-7">
                        <input type="radio" class="col-sm-1" name="finished"  placeholder="finished" value="true"/>
                        <div class="col-sm">Yes</div>
                        <input type="radio" class="col-sm-1" name="finished"  placeholder="finished" value="false"/>
                        <div class="col-sm">No</div>
                    </div>

                    <div class="form-group">
                        <input type="submit" class="btn btn-primary" value="Save"/>
                    </div>
                </div>
            </form>
        </div>
    </div>

这是MainController

@Controller
@RequestMapping("/")
public class MainController {

    @Autowired
   private TaskService taskService;

    @RequestMapping(method = RequestMethod.GET)
    public String home(Model model){
        model.addAttribute("mode", "MODE_HOME");
        return "index";
    }

    @RequestMapping(method = RequestMethod.GET, value = "/all-tasks")
    public String allTasks(Model model){
        model.addAttribute("tasks", taskService.findAll());
        model.addAttribute("mode", "MODE_TASKS");
        return "index";
    }

    @RequestMapping(method = RequestMethod.GET, value = "/new-task")
    public String newTask(Model model){
        //List<Task> taskList = taskService.findAll();
        model.addAttribute("mode", "MODE_NEW");
        return "index";
    }

    @RequestMapping(method = RequestMethod.GET, value = "/save-task")
    @PostMapping("/save-task")
    public String saveTask(@ModelAttribute Task task, Model model) {
        taskService.save(task);
        model.addAttribute("tasks", taskService.findAll());
        model.addAttribute("mode", "MODE_TASKS");
        return "index";
    }

    @RequestMapping(method = RequestMethod.GET, value = "/update-task")
    public String updateTask(@RequestParam int id, Model model){
        model.addAttribute("tasks", taskService.findTask(id));
        model.addAttribute("mode", "MODE_UPDATE");
        return "index";
    }

    @RequestMapping(method = RequestMethod.GET, value = "/delete-task")
    public String deleteTask(@RequestParam (required = false) int id, Model model){
        taskService.delete(id);
        model.addAttribute("tasks", taskService.findAll());
        model.addAttribute("mode", "MODE_TASKS");
        return "index";
    }

}