mybatis返回数据类型为map，值为null的key没返回

<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN"
"https://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
    <settings>  
    	<!-- 当返回数据类型为map，设置callSettersOnNulls会把值为null的key也返回 -->
        <setting name="callSettersOnNulls" value="true"/>  
    </settings> 
</configuration>
<?xml version="1.0"