diff -r 0a2762d83c53 -r be5e86c80628 mercurial/hg.py
--- a/mercurial/hg.py	Tue Jul 06 15:05:03 2010 +0900
+++ b/mercurial/hg.py	Fri Jul 02 15:05:21 2010 +0900
@@ -221,7 +221,7 @@
         src_repo = repository(ui, source)
     else:
         src_repo = source
-        branch = None
+        branch = (None, [])
         origsource = source = src_repo.url()
     rev, checkout = addbranchrevs(src_repo, src_repo, branch, rev)