diff -r 512ba8f37bd4 -r 3231fd2fa7a5 server/serverconfig.py
--- a/server/serverconfig.py	Thu Mar 12 14:21:36 2015 +0100
+++ b/server/serverconfig.py	Wed Mar 18 14:41:47 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,