admin: fixed domain quota display when db not ready.

see #1174

modoboa/admin/models/mailbox.py

@@ -31,8 +31,10 @@ class QuotaManager(models.Manager):
         """Return current usage for domain."""
         qset = self.get_queryset().filter(
             username__endswith="@{}".format(domain.name))
-        result = qset.aggregate(usage=models.Sum("bytes"))
-        return result.get("usage", 0)
+        result = qset.aggregate(usage=models.Sum("bytes")).get("usage", 0)
+        if result is None:
+            result = 0
+        return result
 
 
 class Quota(models.Model):

modoboa/admin/tests/test_domain.py

@@ -257,6 +257,13 @@ class DomainTestCase(ModoTestCase):
         self.assertEqual(response.status_code, 200)
         self.assertNotIn("Usage", response.content.decode())
 
+        # Try with a fresh domain (see #1174)
+        domain = factories.DomainFactory(name="simpson.com", quota=100)
+        url = reverse("admin:domain_detail", args=[domain.pk])
+        response = self.client.get(url)
+        self.assertEqual(response.status_code, 200)
+        self.assertIn("Usage", response.content.decode())
+
     def test_statitics_widget(self):
         """Test statistics display in dashboard."""
         url = reverse("core:dashboard")