diff -r d8a208f7e3d1 -r f7dfcb3add15 server/serverconfig.py
--- a/server/serverconfig.py	Mon Mar 09 09:32:11 2015 +0100
+++ b/server/serverconfig.py	Wed Feb 11 12:42:19 2015 +0100
@@ -237,7 +237,7 @@
           }),
          ('zmq-address-sub',
           {'type' : 'csv',
-           'default' : None,
+           'default' : (),
            'help': ('List of ZMQ addresses to subscribe to (requires pyzmq) '
                     '(of the form `tcp://<ipaddr>:<port>`)'),
            'group': 'zmq', 'level': 1,