Comment 0 for bug 1588846

Testing b6, I was watching the logs and noticed this. Nothing specifically was being done.

==> /var/log/maas/regiond.log <==
2016-06-03 22:38:00 [maas.websocket.listener] Unhandled Error
        Traceback (most recent call last):
          File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 434, in errback
            self._startRunCallbacks(fail)
          File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 501, in _startRunCallbacks
            self._runCallbacks()
          File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 588, in _runCallbacks
            current.result = callback(current.result, *args, **kw)
          File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 1184, in gotResult
            _inlineCallbacks(r, g, deferred)
        --- <exception caught here> ---
          File "/usr/lib/python3/dist-packages/twisted/internet/defer.py", line 1126, in _inlineCallbacks
            result = result.throwExceptionIntoGenerator(g)
          File "/usr/lib/python3/dist-packages/twisted/python/failure.py", line 389, in throwExceptionIntoGenerator
            return g.throw(self.type, self.value, self.tb)
          File "/usr/lib/python3/dist-packages/maasserver/websockets/protocol.py", line 417, in onNotify
            self.processNotify, handler, channel, action, obj_id)
          File "/usr/lib/python3/dist-packages/twisted/python/threadpool.py", line 246, in inContext
            result = inContext.theWork()
          File "/usr/lib/python3/dist-packages/twisted/python/threadpool.py", line 262, in <lambda>
            inContext.theWork = lambda: context.call(ctx, func, *args, **kw)
          File "/usr/lib/python3/dist-packages/twisted/python/context.py", line 118, in callWithContext
            return self.currentContext().callWithContext(ctx, func, *args, **kw)
          File "/usr/lib/python3/dist-packages/twisted/python/context.py", line 81, in callWithContext
            return func(*args,**kw)
          File "/usr/lib/python3/dist-packages/provisioningserver/utils/twisted.py", line 937, in callInContext
            return func(*args, **kwargs)
          File "/usr/lib/python3/dist-packages/maasserver/utils/orm.py", line 516, in call_within_transaction
            return func_outside_txn(*args, **kwargs)
          File "/usr/lib/python3/dist-packages/maasserver/utils/orm.py", line 343, in retrier
            return func(*args, **kwargs)
          File "/usr/lib/python3.5/contextlib.py", line 30, in inner
            return func(*args, **kwds)
          File "/usr/lib/python3/dist-packages/maasserver/websockets/protocol.py", line 424, in processNotify
            return handler.on_listen(channel, action, obj_id)
          File "/usr/lib/python3/dist-packages/maasserver/websockets/base.py", line 437, in on_listen
            pk = self._meta.pk_type(pk)
        builtins.ValueError: invalid literal for int() with base 10: ''