Issues with @cached(type='memory') and no Accept-Language header

With the following setup:

add a method to a controller with @cached(type='memory')
encountered in tg version 2.3.11
running on Docker image python:3.6-alpine.

I guess it could still be present in other releases as well.

The below command works as expected:

curl http://localhost/api/cached_endpoint?version=2 -H "Accept-Language: en-US"

This generates the traceback you can see at the end:

curl http://localhost/api/cached_endpoint?version=2

Is it possible to have a fix for it? I know browsers already add these for you, but other libraries, like Android's Volley do not do this by default. Would it be possible to have a fix?

Traceback (most recent call last):
  File "/usr/local/lib/python3.6/site-packages/tg/wsgiapp.py", line 120, in __call__
    response = self.wrapped_dispatch(controller, environ, context)
  File "/usr/local/lib/python3.6/site-packages/tg/appwrappers/errorpage.py", line 63, in __call__
    resp = self.next_handler(controller, environ, context)
  File "/usr/local/lib/python3.6/site-packages/tg/appwrappers/mingflush.py", line 52, in __call__
    resp = self.next_handler(controller, environ, context)
  File "/usr/local/lib/python3.6/site-packages/tg/appwrappers/caching.py", line 54, in __call__
    return self.next_handler(controller, environ, context)
  File "/usr/local/lib/python3.6/site-packages/tg/appwrappers/session.py", line 71, in __call__
    response = self.next_handler(controller, environ, context)
  File "/usr/local/lib/python3.6/site-packages/tg/appwrappers/identity.py", line 47, in __call__
    return self.next_handler(controller, environ, context)
  File "/usr/local/lib/python3.6/site-packages/tg/appwrappers/i18n.py", line 68, in __call__
    languages.extend(map(sanitize_language_code, context.request.languages))
  File "/usr/local/lib/python3.6/site-packages/tg/caching.py", line 48, in __get__
    return self._get_value(obj)
  File "/usr/local/lib/python3.6/site-packages/tg/caching.py", line 39, in _get_value
    value = self.func(obj)
  File "/usr/local/lib/python3.6/site-packages/tg/request_local.py", line 78, in languages
    return self.languages_best_match(self._language)
  File "/usr/local/lib/python3.6/site-packages/tg/request_local.py", line 37, in languages_best_match
    items = [i for i, q in sorted(al._parsed, key=lambda iq: -iq[1])]
TypeError: 'NoneType' object is not iterable

TurboGears / tg2

Issues with @cached(type='memory') and no Accept-Language header #109