diff -r 2b7a75ca6913 -r b1ae33b813cb mercurial/hg.py
--- a/mercurial/hg.py	Wed Aug 11 12:29:20 2010 +0200
+++ b/mercurial/hg.py	Fri Jul 02 15:12:50 2010 +0900
@@ -221,7 +221,7 @@
         src_repo = repository(ui, source)
     else:
         src_repo = source
-        branch = (None, [])
+        branch = (None, branch or [])
         origsource = source = src_repo.url()
     rev, checkout = addbranchrevs(src_repo, src_repo, branch, rev)