diff -r 43186df4bb8e -r 7af92e70bb25 mercurial/commands.py
--- a/mercurial/commands.py	Sun May 17 03:40:54 2009 +0200
+++ b/mercurial/commands.py	Sun May 17 03:49:59 2009 +0200
@@ -503,7 +503,7 @@
         # create the right base
         # XXX: nodesbetween / changegroup* should be "fixed" instead
         o = []
-        has = {nullid: None}
+        has = set((nullid,))
         for n in base:
             has.update(repo.changelog.reachable(n))
         if revs: