source is null for getProperty(null, "cpmodel")异常结局

org.mybatis.spring.MyBatisSystemException: nested exception is org.apache.ibatis.builder.BuilderException: Error evaluating expression 'requestMap.cpmodel != null and requestMap.cpmodel != '''. Cause: org.apache.ibatis.ognl.OgnlException: source is null for getProperty(null, "cpmodel")

问题出现的愿意：我在mapper.xml中的查询方法中<if></if>中的test里使用了requestMap

代码如下：

<select id="countdoid" resultMap="detailsout">
            select count(doid) from details_out,orders_need_supplyofgoods_details,position,orders_need,product,customer
            where orders_need_supplyofgoods_details.status != 6
            AND details_out.positionid = position.positionid
            AND orders_need_supplyofgoods_details.nid = orders_need.nid
            AND orders_need.cpid = product.cpid
            AND position.cid = customer.cid
            AND details_out.onsdid = orders_need_supplyofgoods_details.onsdid
             <if test="requestMap.cpmodel != null and requestMap.cpmodel != ''">
                AND product.cpmodel = #{requestMap.cpmodel}
            </if>
            <if test="requestMap.cname != null and requestMap.cname != ''">
                AND customer.cname = #{requestMap.cname}
            </if>
            <if test="requestMap.weiyibiaoshi != null and requestMap.weiyibiaoshi != ''">
                AND orders_need_supplyofgoods_details.weiyibiaoshi = #{requestMap.weiyibiaoshi}
            </if>
            <if test="requestMap.status != null and requestMap.status != ''">
                AND orders_need_supplyofgoods_details.status = #{requestMap.status}
            </if>
    </select>

问题解决：我在mapper层中的方法里没有添加@Param("requestMap")Map<String, Object> requestMap,

解决方法：   

　 /**
     *
     * @Title: countdoid
     * @Description: TODO(物资闲置，计算已分发物资的数量)
     * @return
     */
    int countdoid();

添加参数后为

    /**
     *
     * @Title: countdoid
     * @Description: TODO(物资闲置，计算已分发物资的数量)
     * @return
     */
    int countdoid(@Param("requestMap")Map<String, Object> requestMap);

这样在mapper.xml的语句中就不会出问题了