diff -r eb7be0e752d9 -r c5b3d3e30de7 mercurial/changelog.py
--- a/mercurial/changelog.py	Fri May 15 16:12:09 2009 +0200
+++ b/mercurial/changelog.py	Sat May 16 11:12:49 2009 +0200
@@ -202,6 +202,11 @@
                   user=None, 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))