--- a/hgext/obsolete.py	Tue Jun 19 17:57:54 2012 +0200
+++ b/hgext/obsolete.py	Wed Jun 20 14:43:20 2012 +0200
@@ -278,6 +278,8 @@
             targetrev = repo[repo._rebasetarget].rev()
             newrevs = set([targetrev])
             for rev, newrev in sorted(repo._rebasestate.items()):
+                if newrev == -2:  # nullmerge
+                    continue
                 oldnode = repo[rev].node()
                 if newrev not in newrevs and newrev >= 0:
                     newnode = repo[newrev].node()