Mybatis使用<foreach collection="***" item="**" open="(" separator="," close=")">问题

昨天在使用：

<foreach collection="userTypes" item="userType" open="(" separator="," close=")">

时出现一个错误，提示SQL错误，检查发现是在“<foreach>”前面的<if></if>判断语句中使用非空字符串判断，而item只接受list，数组和map,所以出错！
<if test="userTypes != null">
AND USERTYPE in
<foreach collection="userTypes" item="userType" open="(" separator="," close=")">
#{userType}
</foreach>
</if>

原始是：
<if test="userTypes != null and '' != userTypes ">
AND USERTYPE in
<foreach collection="userTypes" item="userType" open="(" separator="," close=")">
#{userType}
</foreach>
</if>