diff -r ca7fa5e5b682 -r 3acc6279b364 mercurial/changelog.py
--- a/mercurial/changelog.py	Sat May 16 08:46:42 2009 +0200
+++ b/mercurial/changelog.py	Sat May 16 11:16:23 2009 +0200
@@ -201,6 +201,11 @@
     def add(self, manifest, files, desc, transaction, p1, p2,
                   user, date=None, extra={}):
         user = user.strip()
+        # An empty username or a username with a "\n" will make the
+        # revision text contain two "\n\n" sequences -> corrupt
+        # repository since read cannot unpack the revision.
+        if not user:
+            raise error.RevlogError(_("empty username"))
         if "\n" in user:
             raise error.RevlogError(_("username %s contains a newline")
                                     % repr(user))