关于Jsp页面的jstl标签的级联属性的异常。

public class Employee
{
    private Integer id;
    private String name;
    private String email;
    private int gender;
    private Department department;
}

public class Department
{
    private Integer id;
    private String departmentName;
}

form:form action="input" method="POST" modelAttribute="employee">
    
        Name: form:input path="name"/>
        br>
        Email: form:input path="email"/>
        br>
        %
            Map> genders = new HashMap();
        
            genders.put(0, "Female");
            genders.put(1, "Male");
            
            request.setAttribute("genders", genders);
        %>
        Gender: form:radiobuttons path="gender" items="${genders}"/>
        br>
        %-- 
            jstl是支持级联属性的，在这里我想选择的部门id，则直接写Employee类中的department属性再".id"就可以了。
            而后面的itemLabel 属性和 itemValue 属性。就不用再加department这个前缀了。直接写Department类的属性名称即可。
            
            Department: ="department.id" items="${departments}" 
            itemLabel="department.departmentName" itemValue="department.id">form:select>
        --%>
        Department: form:select path="department.id" items="${departments}" 
        itemLabel="departmentName" itemValue="id">form:select>
        br>
        input type="submit" name="Submit">
        br>
    form:form>

org.apache.jasper.JasperException: An exception occurred processing JSP page /WEB-INF/views/input.jsp at line 39

36:             Department: form:select path="department.id" items="${departments}" 
37:             itemLabel="department.departmentName" itemValue="department.id">form:select>
38:         --%>
39:         Department: form:select path="department.id" items="${departments}" 
40:         itemLabel="department.departmentName" itemValue="department.id">form:select>
41:         br>
42:         input type="submit" name="Submit">

org.springframework.beans.NotReadablePropertyException: Invalid property ‘department‘ of bean class [com.zcd.ssh.beans.Department]: Bean property ‘department‘ is not readable or has an invalid getter method: Does the return type of the getter match the parameter type of the setter?
    org.springframework.beans.AbstractNestablePropertyAccessor.getPropertyValue(AbstractNestablePropertyAccessor.java:633)
    org.springframework.beans.AbstractNestablePropertyAccessor.getNestedPropertyAccessor(AbstractNestablePropertyAccessor.java:850)
    org.springframework.beans.AbstractNestablePropertyAccessor.getPropertyAccessorForPropertyPath(AbstractNestablePropertyAccessor.java:827)
    org.springframework.beans.AbstractNestablePropertyAccessor.getPropertyValue(AbstractNestablePropertyAccessor.java:622)
    org.springframework.web.servlet.tags.form.OptionWriter.doRenderFromCollection(OptionWriter.java:202)
    org.springframework.web.servlet.tags.form.OptionWriter.renderFromCollection(OptionWriter.java:180)
    org.springframework.web.servlet.tags.form.OptionWriter.writeOptions(OptionWriter.java:133)