--- a/hgext/obsolete.py	Wed Sep 14 19:20:38 2011 +0200
+++ b/hgext/obsolete.py	Wed Sep 14 19:52:57 2011 +0200
@@ -87,7 +87,7 @@
 from mercurial import discovery
 from mercurial import error
 from mercurial import commands
-from mercurial.node import hex, bin, short
+from mercurial.node import hex, bin, short, nullid
 from mercurial.lock import release
 
 ### Patch changectx
@@ -255,6 +255,8 @@
         <subject-full-hex> <object-full-hex>\n"""
     for sub, objs in obssubrels.iteritems():
         for obj in objs:
+            if sub is None:
+                sub = nullid
             flike.write('%s %s\n' % (hex(sub), hex(obj)))
 
 def _obsdeserialise(flike):
@@ -264,7 +266,10 @@
     rels = {}
     for line in flike:
         subhex, objhex = line.split()
-        rels.setdefault(bin(subhex), set()).add(bin(objhex))
+        subnode = bin(subhex)
+        if subnode == nullid:
+            subnode = None
+        rels.setdefault( subnode, set()).add(bin(objhex))
     return rels
 
 def reposetup(ui, repo):
@@ -291,6 +296,8 @@
 
         def addobsolete(self, sub, obj):
             """Add a relation marking that node <sub> is a new version of <obj>"""
+            if sub == nullid:
+                sub = None
             self._obssubrels.setdefault(sub, set()).add(obj)
             self._obsobjrels.setdefault(obj, set()).add(sub)
             try: