Do not verify empty volumes info on Replica update.

coriolis/tasks/replica_tasks.py

@@ -620,11 +620,12 @@ class UpdateDestinationReplicaTask(base.TaskRunner):
             destination_provider.check_update_destination_environment_params(
                 ctxt, destination_connection_info, export_info, volumes_info,
                 old_destination_env, new_destination_env))
-        schemas.validate_value(
-            volumes_info, schemas.CORIOLIS_VOLUMES_INFO_SCHEMA)
 
-        volumes_info = _check_ensure_volumes_info_ordering(
-            export_info, volumes_info)
+        if volumes_info:
+            schemas.validate_value(
+                volumes_info, schemas.CORIOLIS_VOLUMES_INFO_SCHEMA)
+            volumes_info = _check_ensure_volumes_info_ordering(
+                export_info, volumes_info)
 
         task_info['volumes_info'] = volumes_info