Steps in which deletion is not supported have to return an empty list
when queried for deleted objects.
diff --git a/planetstack/openstack_observer/steps/sync_images.py b/planetstack/openstack_observer/steps/sync_images.py
index 2c24e83..9b915fb 100644
--- a/planetstack/openstack_observer/steps/sync_images.py
+++ b/planetstack/openstack_observer/steps/sync_images.py
@@ -9,7 +9,12 @@
     provides=[Image]
     requested_interval=0
 
-    def fetch_pending(self):
+    def fetch_pending(self, deleted):
+        # Images come from the back end
+        # You can't delete them
+        if (deleted):
+            return []
+
         # get list of images on disk
         images_path = Config().observer_images_directory 
         available_images = {}