springboot+MyBatis返回Map时值为null的字段会丢失

public SqlSessionFactory firstSqlSessionFactory(@Qualifier("firstDataSource") DataSource datasource)
          throws Exception {
      SqlSessionFactoryBean bean = new SqlSessionFactoryBean();
      bean.setDataSource(datasource);
      //------------------------------------------------加入的代码开始------------------------------------------------
      org.apache.ibatis.session.Configuration configuration = new org.apache.ibatis.session.Configuration();
      configuration.setCallSettersOnNulls(true);
             bean.setConfiguration(configuration);
      //------------------------------------------------加入的代码结束------------------------------------------------
      bean.setMapperLocations(
      // 设置mybatis的xml所在位置
      new PathMatchingResourcePatternResolver().getResources("classpath*:mapper/first/*.xml"));
      return bean.getObject();
  }