In json package documentation :
Pointer values encode as the value pointed to. A nil pointer encodes as the null JSON object.
So you can store a pointer to a string which will be encoded as a string if not nil and will be encoded as “null” if nil
type student struct {
FirstName *string `json:"first_name"`
MiddleName *string `json:"middle_name"`
LastName *string `json:"last_name"`
}