Not sure why but this fixes a bug we've been seeing:
File "venv/lib/python3.6/site-packages/thorn/events.py", line 124, in send
timeout=timeout, on_timeout=on_timeout,
File "venv/lib/python3.6/site-packages/thorn/events.py", line 146, in _send
allow_keepalive=self.allow_keepalive,
File "venv/lib/python3.6/site-packages/thorn/dispatch/base.py", line 73, in send
**kwargs
File "venv/lib/python3.6/site-packages/vine/synchronization.py", line 57, in __init__
[self.add_noincr(p) for p in promises or []]
File "venv/lib/python3.6/site-packages/vine/synchronization.py", line 57, in <listcomp>
[self.add_noincr(p) for p in promises or []]
File "venv/lib/python3.6/site-packages/vine/synchronization.py", line 82, in add_noincr
p.then(self)
AttributeError: 'NoneType' object has no attribute 'then'
Not sure why but this fixes a bug we've been seeing: