--- a/mercurial/cmdutil.py	Mon Nov 27 22:03:36 2006 -0200
+++ b/mercurial/cmdutil.py	Mon Nov 27 22:56:26 2006 -0200
@@ -45,7 +45,7 @@
     """Yield revision as strings from a list of revision specifications."""
 
     def revfix(repo, val, defval):
-        if not val and val != 0:
+        if not val and val != 0 and defval is not None:
             return defval
         return repo.changelog.rev(repo.lookup(val))