The controller is missing a value.

<tbody>
    <trth:each="User:${userList}">
        <td class="text-center">
            <divth:switch="${User.plan}">
                <pth:case="'plann'">Preparing</p>
            </div>

            <div th:case="'Save'">
                <a href="'>Save</a>
            </div>

            <div th:case="'Submit'">
                <a href=">Submit</a>
            </div>

            <div th:case="'Cancel'">
                <a href=">Cancel</a>
            </div>

            <div th:case="*">
                <a href="">Refer to </a>
            </div>-->   
        </td>
<tbody>

package com.example.demo;

import java.util.ArrayList;
import java.util.List;

import org.springframework.stereotype.Controller;
import org.springframework.ui.Model;
import org.springframework.web.bind.announcement.RequestMapping;

@ Controller
public class test {

    @RequestMapping(value="user")

    public String User (Model Model) {

        List<User>pro=new ArrayList<User>();

        Mission P = new Mission();

        Model.addAttribute("userList", P);

        return "userList.html";
    }

}

package com.example.demo;

public class User {

    private String plan; 

    public User() {
        This.plan="Submit";
    }

    public String getplan() {
        return MissionSt;
    }

    public void setplan(String missionSt){
        MissionSt = missionSt;
    }