go xorm存库处理null值问题

func main() {
	db, err := NewDBCnn()
	if err != nil {
		fmt.Println(err.Error())
		return
	}
	var a int = 13
	b1 := &ModelUser{
		Id:      431,
		Name:    "测试新增2",
		Age:     &a,
		Passwd:  nil,
		Created: "",
		Updated: "",
	}
	db.Insert(b1)

	bean := new(ModelUser)
	rows, err := db.Rows(bean)
	if err != nil {
		fmt.Println(err.Error())
	}
	defer rows.Close()
	var ret = make(map[int64]ModelUser)

	for rows.Next() {
		bean = new(ModelUser)
		rows.Scan(bean)

		ret[bean.Id] = *bean
	}
	for _, v := range ret {
		fmt.Println(fmt.Sprintf("%v", v))
	}
	test, _ := json.Marshal(ret)
	fmt.Println(string(test))

}

// NewDBCnn 新建数据库连接
func NewDBCnn() (*xorm.Engine, error) {

	engine, err := xorm.NewEngine("mysql", "root:localsense@tcp(127.0.0.1:3306)/test?charset=utf8")
	if err != nil {
		// 处理连接错误
	}

	return engine, err
}

type ModelUser struct {
	Id      int64   `xorm:"id" json:"id"`
	Name    string  `xorm:"name" json:"name"`
	Salt    *string `xorm:"salt" json:"salt"`
	Age     *int    `xorm:"age" json:"age"`
	Passwd  *int    `xorm:"passwd" json:"passwd,omitempty"`
	Created string  `xorm:"created" json:"created,omitempty"`
	Updated string  `xorm:"updated" json:"updated,omitempty"`
}

func (e ModelUser) TableName() string {
	return "user"
}