Fix partial PATCH for gift cards (PRETIXEU-75P)

src/pretix/api/serializers/organizer.py

@@ -114,20 +114,21 @@ class GiftCardSerializer(I18nAwareModelSerializer):
 
     def validate(self, data):
         data = super().validate(data)
-        s = data['secret']
-        qs = GiftCard.objects.filter(
-            secret=s
-        ).filter(
-            Q(issuer=self.context["organizer"]) | Q(
-                issuer__gift_card_collector_acceptance__collector=self.context["organizer"])
-        )
-        if self.instance:
-            qs = qs.exclude(pk=self.instance.pk)
-        if qs.exists():
-            raise ValidationError(
-                {'secret': _(
-                    'A gift card with the same secret already exists in your or an affiliated organizer account.')}
+        if 'secret' in data:
+            s = data['secret']
+            qs = GiftCard.objects.filter(
+                secret=s
+            ).filter(
+                Q(issuer=self.context["organizer"]) | Q(
+                    issuer__gift_card_collector_acceptance__collector=self.context["organizer"])
             )
+            if self.instance:
+                qs = qs.exclude(pk=self.instance.pk)
+            if qs.exists():
+                raise ValidationError(
+                    {'secret': _(
+                        'A gift card with the same secret already exists in your or an affiliated organizer account.')}
+                )
         return data
 
     class Meta:

src/tests/api/test_giftcards.py

@@ -147,6 +147,17 @@ def test_giftcard_patch(token_client, organizer, event, giftcard):
     assert giftcard.currency == "EUR"
     assert not giftcard.testmode
 
+    resp = token_client.patch(
+        '/api/v1/organizers/{}/giftcards/{}/'.format(organizer.slug, giftcard.pk),
+        {
+            'value': '9.00',
+        },
+        format='json'
+    )
+    assert resp.status_code == 200
+    giftcard.refresh_from_db()
+    assert giftcard.value == Decimal('9.00')
+
 
 @pytest.mark.django_db
 def test_giftcard_patch_min_value(token_client, organizer, event, giftcard):