fix: always include grant card in Plain customer cards response

When Plain requests the grant card via cardKeys, always include it in
the response even when the user doesn't exist. Previously, if the user
was not found, we returned an empty cards array. Now we return an empty
grant card ({key: "grant", components: []}) to match Plain's expectation
that all requested card keys are always present in the response.

Closes #4553

Co-authored-by: Marco Acierno <marcoacierno@users.noreply.github.com>

Author: github-actions[bot]

backend/integrations/tests/test_views.py

@@ -70,7 +70,7 @@ def test_cannot_get_plain_customer_cards_when_user_doesnt_exist(rest_api_client)
     )
 
     assert response.status_code == 200
-    assert response.data == {"cards": []}
+    assert response.data == {"cards": [{"key": "grant", "components": []}]}
 
 
 @override_settings(PLAIN_INTEGRATION_TOKEN="secret")

backend/integrations/views.py

@@ -30,11 +30,11 @@ def plain_customer_cards(request):
 
     user = User.objects.filter(email=customer_email).first()
 
-    if not user:
-        return Response({"cards": []})
-
     cards = []
     if "grant" in card_keys:
-        cards.append(create_grant_card(request, user, conference))
+        if user:
+            cards.append(create_grant_card(request, user, conference))
+        else:
+            cards.append({"key": "grant", "components": []})
 
     return Response({"cards": cards})