Thymeleaf和Spring的对象绑定无法正常工作

Question

我有Project个对象，其中包含带有Roles对象的列表Role。我想使用表单编辑项目。此表单需要包含角色清单。所以我将Project对象与th:object绑定在一起。现在，当用户选中复选框并保存时，它会因错误而失败。

表单以呈现复选框

<ul class="checkbox-list">
  <li th:each="role,stat : ${allRoles}">
        <input type="checkbox" th:value="${role.id}" th:field="*{roles[__${stat.index}__].id}"/>
        <span class="primary" th:text="${role.name}"> Developer</span>
   </li>
</ul>

项目对象

public class Project {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY)
int id;
String name;
String description;
private String status;
private String slug;


@ManyToMany
List<Role> roles = new ArrayList<>();

@ManyToMany
List<Collaborator> collaborators = new ArrayList<>();
................
................
}

角色对象：

@Entity
public class Role {
@Id
@GeneratedValue(strategy = GenerationType.IDENTITY )
private int id;
private String name;
.............
.............
.............
}

相关控制器方法

@RequestMapping("/edit-project/{slug}")
    public String editProjectFromSlug(@PathVariable String slug,Model model) {
        Project project = projectService.findProjectBySlug(slug);
        List<Role> allRoles = roleService.getAllRoles();
        //Two objects are added to the model
        model.addAttribute("project",project);
        model.addAttribute("allRoles",allRoles);
        return "edit_project";
    }

@RequestMapping(value = "/save-project", method = RequestMethod.POST)
public String saveProject(@ModelAttribute Project project,Model model){
    projectService.saveProject(project);
    return "redirect:/projects";
}

我已经提到了多个答案，例如this。他们都没有工作。代码位于此github repo。请帮我修复此错误。