Background process 'expire_url_cache_data' threw an exception

[richvdh]

I'm seeing this every few seconds:

2020-03-31 12:30:15,350 - synapse.rest.media.v1.preview_url_resource - 401 - INFO - expire_url_cache_data-1 - Running url preview cache expiry
2020-03-31 12:30:15,351 - synapse.metrics.background_process_metrics - 215 - ERROR - expire_url_cache_data-1 - Background process 'expire_url_cache_data' threw an exception
Traceback (most recent call last):
  File "/home/rav/work/synapse/env3/lib/python3.6/site-packages/twisted/internet/defer.py", line 1418, in _inlineCallbacks
    result = g.send(result)
StopIteration: []

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/rav/work/synapse/env3/lib/python3.6/site-packages/twisted/internet/defer.py", line 1418, in _inlineCallbacks
    result = g.send(result)
StopIteration: []

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/rav/work/synapse/synapse/metrics/background_process_metrics.py", line 213, in run
    return (yield result)
  File "/home/rav/work/synapse/env3/lib/python3.6/site-packages/twisted/internet/defer.py", line 1418, in _inlineCallbacks
    result = g.send(result)
  File "/home/rav/work/synapse/synapse/rest/media/v1/preview_url_resource.py", line 430, in _expire_url_cache_data
    await self.store.delete_url_cache(removed_media)
TypeError: object NoneType can't be used in 'await' expression

[richvdh]

looks like this was introduced in #7110, though I'm a bit surprised by the error message. delete_url_cache returns a Deferred, not a None.

[richvdh]

scratch that, sometimes it returns a None.

[clokep]

Should be fixed in #7184.

[richvdh]

there's another one I'm afraid:

Traceback (most recent call last):
  File "/opt/synapse/synapse/synapse/metrics/background_process_metrics.py", line 213, in run
    return (yield result)
  File "/opt/synapse/env3/lib/python3.5/site-packages/twisted/internet/defer.py", line 1418, in _inlineCallbacks
    result = g.send(result)
  File "/opt/synapse/synapse/synapse/rest/media/v1/preview_url_resource.py", line 478, in _expire_url_cache_data
    await self.store.delete_url_cache_media(removed_media)
TypeError: object NoneType can't be used in 'await' expression

[richvdh]

fixed in #7241