mybatisplus分页查询问题

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@TableName("t_dept")
@Data
@NoArgsConstructor
@AllArgsConstructor
@Builder
public class Dept {
    @TableId
    private Integer id;
    private String name;
    private String userCount;
    private List<Employee> emps;
}

public interface DeptMapper extends BaseMapper<Dept> {
    public IPage<Dept> getPage3(Page<Dept> deptIPage);
}

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="com.study.mapper.DeptMapper">
    <select id="getPage3" resultMap="resMap2">
        SELECT d.id as id,d.name as name,
        e.id AS e_id ,e.name AS e_name,e.dept_id as e_deptId
        FROM t_dept d JOIN t_employee e ON d.id = e.dept_id
    </select>
    <resultMap id="resMap2" type="com.study.bean.Dept">
        <id column="id" property="id"/>
        <result column="name" property="name"/>
        <result column="user_count" property="userCount"/>
        <collection property="emps" ofType="Employee">
            <id column="e_id" property="id"/>
            <result column="e_name" property="name"/>
            <result column="e_deptId" property="deptId"/>
        </collection>
    </resultMap>
</mapper>

@RunWith(SpringRunner.class)
@SpringBootTest
public class MybatisTest {

    @Autowired
    DeptMapper deptMapper;
    @Test
    public void testPage4(){
        Page<Dept> page = new Page<>();
        page.setSize(3);
        page.setCurrent(1);
        IPage<Dept> page3 = deptMapper.getPage3(page);
        System.out.println(JSONUtil.toJsonStr(page3));
    }
}

以前在mybatis中是可以合并这个数据的，不知道mybatisplus为什么不可以了。