From 6cd8d5cfe9d56a062a0aec99d4711348b3b4333f 2015-03-28 00:03:46
From: Sylvain Corlay <sylvain.corlay@gmail.com>
Date: 2015-03-28 00:03:46
Subject: [PATCH] missing allow_none=True

---

diff --git a/IPython/kernel/zmq/session.py b/IPython/kernel/zmq/session.py
index 5769954..0ecb299 100644
--- a/IPython/kernel/zmq/session.py
+++ b/IPython/kernel/zmq/session.py
@@ -341,7 +341,7 @@ class Session(Configurable):
     def _digest_mod_default(self):
         return hashlib.sha256
     
-    auth = Instance(hmac.HMAC)
+    auth = Instance(hmac.HMAC, allow_none=True)
     
     def _new_auth(self):
         if self.key: