MarshalJSON marshals to an empty `{}` for value types

[OmarTariq612]

Unmarshaling works flawlessly, but when marshaling a value (not a pointer) the outcome is {} because MarshalJSON is implemented for a pointer reciever not a value reciever, is this intended ? if so, could you explain why is it implemented that way ?

Using this example: here is the playground link: https://go.dev/play/p/59r5A-OJtUl

package main

import (
	"encoding/json"
	"fmt"

	orderedmap "github.com/wk8/go-ordered-map/v2"
)

func main() {
	b := []byte(`
	{
		"key_1": "value_1",
		"key_2": "value_2"
	}
	`)

	var s orderedmap.OrderedMap[string, string]
	if err := json.Unmarshal(b, &s); err != nil {
		panic(err)
	}

	for pair := s.Oldest(); pair != nil; pair = pair.Next() {
		fmt.Println(pair.Key, pair.Value)
		// this prints:
		// key_1 value_1
		// key_2 value_2
	}

	b, err := json.Marshal(s)
	if err != nil {
		panic(err)
	}

	fmt.Println(string(b)) // this prints: {}
}