--- a/hgext/simple4server.py	Wed Aug 27 10:49:58 2014 +0200
+++ b/hgext/simple4server.py	Wed Aug 27 12:02:53 2014 +0200
@@ -226,7 +226,8 @@
     (special case so that all empty are hashed as nullid)"""
     hashs = _obsrelsethashtree(repo)
     nm = repo.changelog.nodemap
-    return  [hashs[nm.get(n)][1] for n in nodes]
+    revs = [nm.get(n) for n in nodes]
+    return [r is None and node.nullid or hashs[r][1] for r in revs]
 
 # from evolve extension: 1a23c7c52a43
 def srv_obshash(repo, proto, nodes):