task() can return None
Observed in BLISS tests:
Traceback (most recent call last):
File "/opt/conda/envs/testenv/lib/python3.7/threading.py", line 926, in _bootstrap_inner
self.run()
File "/opt/conda/envs/testenv/lib/python3.7/site-packages/Lima/Server/plugins/Bpm.py", line 628, in run
while self._task()._stop is False:
AttributeError: 'NoneType' object has no attribute '_stop'