--- a/hgext/inhibit.py	Wed May 13 09:03:11 2015 -0700
+++ b/hgext/inhibit.py	Thu May 14 15:59:06 2015 -0700
@@ -160,7 +160,8 @@
     Public changesets are already immune to obsolescence"""
     getrev = repo.changelog.nodemap.get
     getphase = repo._phasecache.phase
-    return (n for n in repo._obsinhibit if getphase(repo, getrev(n)))
+    return (n for n in repo._obsinhibit
+            if getrev(n) is not None and getphase(repo, getrev(n)))
 
 def _inhibitmarkers(repo, nodes):
     """add marker inhibitor for all obsolete revision under <nodes>