<!-- 是否品牌客户  品牌字段不为空 -->
<if test="brandCustomer != null">
    <if test="brandCustomer == '是'">
       and (c.brand is not null and c.brand !='')
    </if>
    <if test="brandCustomer == '否'">
        and (c.brand is null or c.brand ='')
    </if>
</if>

执行报错

<!-- 是否品牌客户  品牌字段不为空 -->
<if test="brandCustomer != null">
    <if test="brandCustomer == '是'.toString()">
       and (c.brand is not null and c.brand !='')
    </if>
    <if test="brandCustomer == '否'.toString()">
        and (c.brand is null or c.brand ='')
    </if>
</if>

因为'' 会转为char

参考文档

if 判断等于一个字符串_mybatis if等于字符串-CSDN博客