slapos_upgrader: instances do not always have a predecessor

master/bt5/slapos_upgrader/SkinTemplateItem/portal_skins/slapos_upgrader/Instance_activateMigrationToRemoteProject.py

@@ -60,7 +60,7 @@ else:
   # invert the instance references, to ensure cdn keep the same domain name
   # as we also want to keep subobject (login), change the instance from one tree into another
   original_predecessor = instance.getSuccessorRelatedValue()
-  assert original_predecessor is not None
+  if original_predecessor is not None:
     successor_list = original_predecessor.getSuccessorList()
     successor_list = [x.replace(instance.getRelativeUrl(), requested_software_instance.getRelativeUrl()) for x in successor_list]
 
@@ -79,6 +79,7 @@ else:
     aggregate_value=remote_partition,
     follow_up_value=remote_instance_tree.getFollowUpValue()
   )
+  if original_predecessor is not None:
     original_predecessor.edit(
       successor_list=successor_list
     )