Mybatis映射问题，始终有这个报错

我的User类里面种包含了一个UserRole类，我的xml映射文件：

我的查询语句：

我的JavaBean：

报错信息：No typehandler found for property userRole

请大神帮帮忙！谢谢

First

<select id="selectBlog" resultMap="blogResult">
  select
  B.id as blog_id,
  B.title as blog_title,
  B.author_id as blog_author_id,
  P.id as post_id,
  P.subject as post_subject,
  P.body as post_body,
  from Blog B
  left outer join Post P on B.id = P.blog_id
  where B.id = #{id}
</select>

then

<resultMap id="blogResult" type="Blog">
  <id property="id" column="blog_id" />
  <result property="title" column="blog_title"/>
  <collection property="posts" ofType="Post">
    <id property="id" column="post_id"/>
    <result property="subject" column="post_subject"/>
    <result property="body" column="post_body"/>
  </collection>
</resultMap>