sql的nullxxx转go基本类型

Question

{

    "code":  0,

    "data":  {

        "employeeId":  101,

        "first_name":   "Neena",

        "last_name":   "Kochhar",

        "email":   "NKOCHHAR",

        "phone_number":   "515.123.4568",

        "job_id.String":  {

            "String":   "AD_VP",

            "Valid":  true   
        },
        "salary":   "17000.00",
        "commission_pct":  {
            "String":   "",
            "Valid":  false     
        },
        "manager_id":  {
            "String":   "100",
            "Valid":  true    
        },
        "department_id":  {
            "String":   "90",
            "Valid":  true     
        },

        "hiredate":   "1992-04-03 00:00:00"
    },
    "msg":   "查询成功"
}

sql的NullString用了之后传给前端是这样的，怎么转成json啊。