diff -r 630caaf29815 -r bd7011246fab mercurial/commands.py
--- a/mercurial/commands.py	Tue Dec 05 16:33:40 2006 +0100
+++ b/mercurial/commands.py	Tue Dec 05 13:41:42 2006 -0800
@@ -2189,7 +2189,7 @@
     necessary.  The file '.hg/localtags' is used for local tags (not
     shared among repositories).
     """
-    if name in ['tip', '.']:
+    if name in ['tip', '.', 'null']:
         raise util.Abort(_("the name '%s' is reserved") % name)
     if rev_ is not None:
         ui.warn(_("use of 'hg tag NAME [REV]' is deprecated, "