diff -r 2631b506e93d -r 000d122071b5 mercurial/cmdutil.py
--- a/mercurial/cmdutil.py	Thu Dec 07 11:22:17 2006 +0100
+++ b/mercurial/cmdutil.py	Thu Dec 07 14:15:11 2006 -0200
@@ -18,7 +18,7 @@
     be None, meaning use working dir.'''
 
     def revfix(repo, val, defval):
-        if not val and val != 0:
+        if not val and val != 0 and defval is not None:
             val = defval
         return repo.lookup(val)