Cannot delete all addons from the subscriptions

[kudrykv]

Describe the bug

There is a subscription with a few addons. The intention is to delete all addons on renewal. To perform this action, this curl suffices:

 curl \
  -u 'apikey:' \
  -H 'Content-Type: application/json' \
  -H 'Accept: application/vnd.recurly.v2021-02-25+json' \
  -X POST \
  -d '{"timeframe": "renewal", "add_ons": []}' \
  'https://v3.recurly.com/subscriptions/uuid-my-uuid/change'

However, there is an issue with the SubscriptionChangeCreate type, AddOns field. Because it is annotated with omitempty (json:"add_ons,omitempty"), the field is not being marshalled even if the array is allocated.

To Reproduce

package play_test

import (
	"os"
	"testing"

	"github.com/recurly/recurly-client-go/v4"
)

func TestRecurlyRemoveLastAddon(t *testing.T) {
	t.Parallel()

	client, err := recurly.NewClient(os.Getenv("RECURLY_API_KEY"))
	if err != nil {
		t.Fatal(err)
	}

	t.Run("remove last addon, initialized empty addon list", func(t *testing.T) {
		t.Parallel()

		renewal := "renewal"
		changeCreate := &recurly.SubscriptionChangeCreate{
			Timeframe: &renewal,
			AddOns:    make([]recurly.SubscriptionAddOnUpdate, 0),
		}

		_, err = client.CreateSubscriptionChange("uuid-70647702d223609410b7a948528e1dad", changeCreate)
		if err != nil {
			t.Fatal(err)
		}
	})
}


func TestSubscriptionChangeCreateMarshal(t *testing.T) {
	t.Parallel()

	item := recurly.SubscriptionChangeCreate{
		AddOns:    make([]recurly.SubscriptionAddOnUpdate, 0),
	}

	jsonBytes, err := json.Marshal(item)
	if err != nil {
		t.Fatal(err)
	}

	if string(jsonBytes) != `{"timeframe":"renewal","add_ons":[]}` {
		t.Fatalf("want != have: %s", string(jsonBytes))
	}
}

In the same time, simply removing omitempty would break the statement from the documentation: If this value is omitted your existing add-ons will be unaffected. By removing omitempty it'll always marshal the value, resulting in either an array of addons, an empty array (if allocated), or in null. Passing null on the endpoint raises Recurly error:

{
  "error": {
    "type": "validation",
    "message": "Please remove the following unpermitted parameters from your request: add_ons.",
    "params":[{"param":"add_ons"}]
  }
}

Expected behavior

Initialized slice being marshalled and addons being removed (on renewal in my case).

Your Environment

• Which version of this library are you using?
  v4.48.0
• Which version of golang are you using?
  1.21

[maciejjwojcik]

Hi, just wanted to bump this. I really need this functionality fixed ASAP.