diff --git a/hgext3rd/perftweaks.py b/hgext3rd/perftweaks.py
--- a/hgext3rd/perftweaks.py
+++ b/hgext3rd/perftweaks.py
@@ -183,7 +183,7 @@
     partial = repo._branchcaches.get(repo.filtername)
     if partial is None:
         partial = branchmap.branchcache()
-    partial.update(repo, None)
+    partial.update(repo, [])
     repo._branchcaches[repo.filtername] = partial
 
 # _docommit accesses "branchheads" just to decide whether to show "(created new