--- a/hgext/obsolete.py	Tue Jun 19 10:24:47 2012 +0200
+++ b/hgext/obsolete.py	Tue Jun 19 18:02:34 2012 +0200
@@ -230,7 +230,11 @@
     """wrapper for rebase 's concludenode that set obsolete relation"""
     newrev = orig(repo, rev, *args, **kwargs)
     oldnode = repo[rev].node()
-    newnode = repo[newrev].node()
+    if newrev is not None:
+        newnode = repo[newrev].node()
+    else:
+        # Revision was emptied and removed, there is no successor.
+        newnode = nullid
     repo.addobsolete(newnode, oldnode)
     return newrev