fix: review fixes

Author: borosr

api/v3/handlers/subscriptions/subscriptionaddons/get.go

@@ -2,6 +2,7 @@ package subscriptionaddons
 
 import (
 	"context"
+	"errors"
 	"net/http"
 
 	apiv3 "github.com/openmeterio/openmeter/api/v3"
@@ -43,6 +44,10 @@ func (h *handler) GetSubscriptionAddon() GetSubscriptionAddonHandler {
 				return GetSubscriptionAddonResponse{}, err
 			}
 
+			if a == nil {
+				return GetSubscriptionAddonResponse{}, models.NewGenericNotFoundError(errors.New("subscription addon not found"))
+			}
+
 			return toAPISubscriptionAddon(*a)
 		},
 		commonhttp.JSONResponseEncoderWithStatus[GetSubscriptionAddonResponse](http.StatusOK),

openmeter/subscription/addon/service.go

@@ -85,13 +85,13 @@ type GetSubscriptionAddonInput struct {
 func (i GetSubscriptionAddonInput) Validate() error {
 	var errs []error
 
-	if err := i.NamespacedID.Validate(); err != nil {
-		errs = append(errs, err)
+	if i.NamespacedID.Namespace == "" {
+		errs = append(errs, errors.New("namespace is required"))
 	}
 
 	if i.ID == "" {
 		if i.SubscriptionID == "" {
-			errs = append(errs, errors.New("subscription id or key must be provided if assignment id is not provided"))
+			errs = append(errs, errors.New("subscription id must be provided if assignment id is not provided"))
 		} else if _, err := ulid.Parse(i.SubscriptionID); err != nil {
 			errs = append(errs, errors.New("subscription id is not a valid ULID"))
 		}