Defferent behavior from "encoding/json" for MarshalJSON

[hidechae]

package main

import (
	"database/sql"
	"encoding/json"
	"fmt"
	goccyjson "github.com/goccy/go-json"
)

func main() {
	v := []struct{
		NS NullString
	}{
		{
			NS: NullString{String:"test", Valid: true},
		},
	}

	got, _ := json.Marshal(v)
	fmt.Println(string(got)) // output: [{"NS":"test"}]

	got, _ = goccyjson.Marshal(v)
	fmt.Println(string(got)) // output: [{"NS":{"String":"test","Valid":true}}]
}

type NullString sql.NullString

func (s *NullString) MarshalJSON() ([]byte, error) {
	if !s.Valid {
		return json.Marshal(nil)
	}
	return json.Marshal(s.String)
}

When I change (s *NullString) to (s NullString), it's fine. (and maybe I should do so.)
So, it is not a critical issue, but I would prefer that compatibility be supported.