Spring MVC - 提交带下拉列表的表单时缺少字段的HTTP状态代码400（错误请求）

I'm using spring mvc with thymeleaf to save a form with a dropdown value. The problem is when saving, I get the error 400 bad request only when I append the foreign key field in the form as a dropdown with I'm using spring mvc with thymeleaf to save a f