get_key_for_task in celery.backends.base fails on AsyncResult(None)

[zupo]

If I instantiate an AsyncResult with None, and then call "res.state", I will get a TypeError. The error occurs because task_id of "res" is None, and one cannot join a list of strings and None.

Traceback:

TypeError: sequence item 1: expected string, NoneType found - 
celery/result.py in state:
celery/result.py in _get_task_meta:
celery/backends/base.py in get_task_meta:
celery/backends/base.py _get_task_meta_for:
celery/backends/base.py in get_key_for_task:
         return key_t('').join([
             self.task_keyprefix, key_t(task_id), key_t(key),
         ])

celery report:

software -> celery:3.1.10 (Cipater) kombu:3.0.14 py:2.7.4
            billiard:3.3.0.14 py-amqp:1.4.4
platform -> system:Linux arch:64bit, ELF imp:CPython
loader   -> celery.loaders.default.Loader
settings -> transport:amqp results:redis://url

CELERY_TRACK_STARTED: True
CELERYD_TASK_TIME_LIMIT: 600.0
BROKER_POOL_LIMIT: 1
CELERY_ACKS_LATE: True
BROKER_URL: 'amqp://url'
CELERYD_CONCURRENCY: 1
CELERY_RESULT_BACKEND: 'redis://url'
CELERY_TIMEZONE: 'UTC'
CELERY_ACCEPT_CONTENT: ['pickle']

[ask]

What would you expect to happen here?

[zupo]

That's a good question indeed. One option would be to return an empty string or None as result.status. The other would be to raise a more descriptive exception. I don't have a good argument as to which one of these is better.

[zupo]

Thanks!