The server encountered an unexpected condition which prevented it from fulfilling the request.
Traceback (most recent call last): File "/usr/local/lib/python2.7/dist-packages/cherrypy/_cprequest.py", line 656, in respond response.body = self.handler() File "/usr/local/lib/python2.7/dist-packages/cherrypy/lib/encoding.py", line 188, in __call__ self.body = self.oldhandler(*args, **kwargs) File "/usr/local/lib/python2.7/dist-packages/cherrypy/_cpdispatch.py", line 34, in __call__ return self.callable(*self.args, **self.kwargs) File "/usr/local/share/neuron/0.2/ncm/controllers.py", line 129, in default return NeuronServer(site).execute(nl, **data) File "/usr/local/share/neuron/0.2/ncm/controllers.py", line 317, in execute if not NeuronMapper(self.site, nl).call(): File "/usr/local/share/neuron/0.2/ncm/controllers.py", line 451, in call handler(**args) File "/usr/local/share/neuron/0.2/ncm/modules/NShop/controllers.py", line 1412, in add_to_cart self.site.redirect_back() File "/usr/local/share/neuron/0.2/ncm/controllers.py", line 217, in redirect_back raise cherrypy.HTTPRedirect(cherrypy.session.get("__referer")) File "/usr/local/lib/python2.7/dist-packages/cherrypy/_cperror.py", line 196, in __init__ for url in urls: TypeError: 'NoneType' object is not iterable