Exception from diff

[dread]

Investigate exception occured occasionally in last couple of days on ckan.net:

WebApp Error: <type 'exceptions.AttributeError'>: 'NoneType' object has no attribute 'key' 					

URL: http://ckan.net/revision/diff/dbtune-audioscrobbler?diff=66a47b9e-232a-4838-8674-66fa1a5c76e1&oldid=a99c98be-767a-4e49-9025-2472b2d18b9c
Module weberror.errormiddleware:162 in __call__
<<              __traceback_supplement__ = Supplement, self, environ
                   sr_checker = ResponseStartChecker(start_response)
                   app_iter = self.application(environ, sr_checker)
                   return self.make_catching_iter(app_iter, environ, sr_checker)
               except:
>>  app_iter = self.application(environ, sr_checker)
Module beaker.middleware:73 in __call__
<<                                                     self.cache_manager)
               environ[self.environ_key] = self.cache_manager
               return self.app(environ, start_response)
>>  return self.app(environ, start_response)
Module beaker.middleware:152 in __call__
<<                          headers.append(('Set-cookie', cookie))
                   return start_response(status, headers, exc_info)
               return self.wrap_app(environ, session_start_response)
           
           def _get_session(self):
>>  return self.wrap_app(environ, session_start_response)
Module routes.middleware:130 in __call__
<<                  environ['SCRIPT_NAME'] = environ['SCRIPT_NAME'][:-1]
               
               response = self.app(environ, start_response)
               
               # Wrapped in try as in rare cases the attribute will be gone already
>>  response = self.app(environ, start_response)
Module pylons.wsgiapp:125 in __call__
<<          
               controller = self.resolve(environ, start_response)
               response = self.dispatch(controller, environ, start_response)
               
               if 'paste.testing_variables' in environ and hasattr(response,
>>  response = self.dispatch(controller, environ, start_response)
Module pylons.wsgiapp:324 in dispatch
<<          if log_debug:
                   log.debug("Calling controller class with WSGI interface")
               return controller(environ, start_response)
           
           def load_test_env(self, environ):
>>  return controller(environ, start_response)
Module ckan.lib.base:73 in __call__
<<          # available in environ['pylons.routes_dict']    
               try:
                   return WSGIController.__call__(self, environ, start_response)
               finally:
                   model.Session.remove()
>>  return WSGIController.__call__(self, environ, start_response)
Module pylons.controllers.core:221 in __call__
<<                  return response(environ, self.start_response)
               
               response = self._dispatch_call()
               if not start_response_called:
                   self.start_response = start_response
>>  response = self._dispatch_call()
Module pylons.controllers.core:172 in _dispatch_call
<<              req.environ['pylons.action_method'] = func
                   
                   response = self._inspect_call(func)
               else:
                   if log_debug:
>>  response = self._inspect_call(func)
Module pylons.controllers.core:107 in _inspect_call
<<                        func.__name__, args)
               try:
                   result = self._perform_call(func, args)
               except HTTPException, httpe:
                   if log_debug:
>>  result = self._perform_call(func, args)
Module pylons.controllers.core:60 in _perform_call
<<          """Hide the traceback for everything above this method"""
               __traceback_hide__ = 'before_and_this'
               return func(**args)
           
           def _inspect_call(self, func):
>>  return func(**args)
Module ckan.controllers.revision:119 in diff
<<          c.revision_to = model.Session.query(model.Revision).get(
                   request.params.getone('diff'))
               diff = pkg.diff(c.revision_to, c.revision_from)
               c.diff = diff.items()
               c.diff.sort()
>>  diff = pkg.diff(c.revision_to, c.revision_from)
Module ckan.model.package:340 in diff
<<                              display_id = to_obj_rev.tag.name
                               elif obj_class.__name__ == 'PackageExtra':
                                   display_id = to_obj_rev.key
                               else:
                                   display_id = related_obj_id[:4]
>>  display_id = to_obj_rev.key
AttributeError: 'NoneType' object has no attribute 'key'
CGI Variables
DOCUMENT_ROOT	'/htdocs'
GATEWAY_INTERFACE	'CGI/1.1'
HTTP_ACCEPT	'*/*'
HTTP_ACCEPT_ENCODING	'gzip'
HTTP_ACCEPT_LANGUAGE	'zh-cn,zh-tw'
HTTP_CONNECTION	'close'
HTTP_HOST	'ckan.net'
HTTP_USER_AGENT	'Baiduspider+(+http://www.baidu.com/search/spider.htm)'
PATH	'/usr/local/bin:/usr/bin:/bin'
PATH_INFO	'/revision/diff/dbtune-audioscrobbler'
PATH_TRANSLATED	'/home/okfn/var/srvc/ckan.net/pyenv/bin/ckan.net.py/revision/diff/dbtune-audioscrobbler'
QUERY_STRING	'diff=66a47b9e-232a-4838-8674-66fa1a5c76e1&oldid=a99c98be-767a-4e49-9025-2472b2d18b9c'
REMOTE_ADDR	'123.125.66.32'
REMOTE_PORT	'63767'
REQUEST_METHOD	'GET'
REQUEST_URI	'/revision/diff/dbtune-audioscrobbler?diff=66a47b9e-232a-4838-8674-66fa1a5c76e1&oldid=a99c98be-767a-4e49-9025-2472b2d18b9c'
SCRIPT_FILENAME	'/home/okfn/var/srvc/ckan.net/pyenv/bin/ckan.net.py'
SCRIPT_URI	'http://ckan.net/revision/diff/dbtune-audioscrobbler'
SCRIPT_URL	'/revision/diff/dbtune-audioscrobbler'
SERVER_ADDR	'10.226.226.118'
SERVER_ADMIN	'[no address given]'
SERVER_NAME	'ckan.net'
SERVER_PORT	'80'
SERVER_PROTOCOL	'HTTP/1.1'
SERVER_SIGNATURE	'<address>Apache/2.2.9 (Debian) mod_wsgi/2.5 Python/2.5.2 Server at ckan.net Port 80</address>\n'
SERVER_SOFTWARE	'Apache/2.2.9 (Debian) mod_wsgi/2.5 Python/2.5.2'
WSGI Variables
application	<beaker.middleware.CacheMiddleware object at 0x9f603ec>
beaker.cache	<beaker.cache.CacheManager object at 0x9f6042c>
beaker.get_session	<bound method SessionMiddleware._get_session of <beaker.middleware.SessionMiddleware object at 0x9f602ac>>
beaker.session	{'_accessed_time': 1282385101.4243281, '_creation_time': 1282385101.4243281}
mod_wsgi.application_group	'ckan.net|'
mod_wsgi.callable_object	'application'
mod_wsgi.listener_host	''
mod_wsgi.listener_port	'80'
mod_wsgi.process_group	''
mod_wsgi.reload_mechanism	'0'
mod_wsgi.script_reloading	'1'
mod_wsgi.version	(2, 5)
paste.cookies	(<SimpleCookie: >, '')
paste.parsed_querystring	([('diff', '66a47b9e-232a-4838-8674-66fa1a5c76e1'), ('oldid', 'a99c98be-767a-4e49-9025-2472b2d18b9c')], 'diff=66a47b9e-232a-4838-8674-66fa1a5c76e1&oldid=a99c98be-767a-4e49-9025-2472b2d18b9c')
paste.registry	<paste.registry.Registry object at 0x104552ec>
paste.throw_errors	True
pylons.action_method	<bound method RevisionController.diff of <ckan.controllers.revision.RevisionController object at 0xfb17aec>>
pylons.controller	<ckan.controllers.revision.RevisionController object at 0xfb17aec>
pylons.environ_config	{'session': 'beaker.session', 'cache': 'beaker.cache'}
pylons.pylons	<pylons.util.PylonsContext object at 0x10286d4c>
pylons.routes_dict	{'action': u'diff', 'controller': u'revision', 'id': u'dbtune-audioscrobbler'}
repoze.who.logger	<logging.Logger instance at 0xa16e0cc>
repoze.who.plugins	{'openid': <OpenIdIdentificationPlugin 167584972>, 'auth_tkt': <AuthTktCookiePlugin 169253516>}
routes.route	<routes.route.Route object at 0x9f3690c>
routes.url	<routes.util.URLGenerator object at 0xfd8d7cc>
webob._parsed_query_vars	(GET([('diff', '66a47b9e-232a-4838-8674-66fa1a5c76e1'), ('oldid', 'a99c98be-767a-4e49-9025-2472b2d18b9c')]), 'diff=66a47b9e-232a-4838-8674-66fa1a5c76e1&oldid=a99c98be-767a-4e49-9025-2472b2d18b9c')
webob.adhoc_attrs	{'language': 'en-us'}
wsgi process	'Multi process AND threads (?)'
wsgi.file_wrapper	<built-in method file_wrapper of mod_wsgi.Adapter object at 0x103a5bf0>
wsgiorg.routing_args	(<routes.util.URLGenerator object at 0xfd8d7cc>, {'action': u'diff', 'controller': u'revision', 'id': u'dbtune-audioscrobbler'})

[rgrp]

Looks like a duplicate of ticket:463 (also added by dread -- so hope I'm not making a mistake!)