diff --git a/nova/api/openstack/placement/util.py b/nova/api/openstack/placement/util.py
index e7185a0a86ad..f20eeef19cf4 100644
--- a/nova/api/openstack/placement/util.py
+++ b/nova/api/openstack/placement/util.py
@@ -640,7 +640,7 @@ def ensure_consumer(ctx, consumer_uuid, project_id, user_id,
             if consumer_generation is not None:
                 raise webob.exc.HTTPConflict(
                     _('consumer generation conflict - '
-                      'expected None but got %s') % consumer_generation)
+                      'expected null but got %s') % consumer_generation)
         # No such consumer. This is common for new allocations. Create the
         # consumer record
         try:
diff --git a/nova/tests/functional/api/openstack/placement/gabbits/allocations-1.28.yaml b/nova/tests/functional/api/openstack/placement/gabbits/allocations-1.28.yaml
index 839ef270835d..c1e356c7da83 100644
--- a/nova/tests/functional/api/openstack/placement/gabbits/allocations-1.28.yaml
+++ b/nova/tests/functional/api/openstack/placement/gabbits/allocations-1.28.yaml
@@ -50,6 +50,21 @@ tests:
   response_strings:
     - JSON does not validate
 
+- name: new version gen is not null no existing
+  PUT: /allocations/22222222-2222-2222-2222-222222222222
+  data:
+      allocations:
+          $ENVIRON['RP_UUID']:
+            resources:
+              DISK_GB: 10
+      project_id: $ENVIRON['PROJECT_ID']
+      user_id: $ENVIRON['USER_ID']
+      consumer_generation: 5
+  status: 409
+  response_strings:
+    - consumer generation conflict
+    - expected null but got 5
+
 - name: new version gen is None no existing
   PUT: /allocations/22222222-2222-2222-2222-222222222222
   data: