python-greenio: FTBFS: RuntimeError: generator raised StopIteration

Imported from Debian bug http://bugs.debian.org/802148:

Source: python-greenio
Version: 0.6.0-1
Severity: serious
Justification: fails to build from source
Tags: sid stretch
User: <email address hidden>
Usertags: ftbfs
X-Debbugs-CC: <email address hidden>

Dear Maintainer,

The package fails to build:

set -e && for pyvers in 3.5 3.4; do \
 python$pyvers runtests.py ; \
done
EE.................E
======================================================================
ERROR: test_asyncio_coroutine (test_asyncio_trollius.TrolliusEventLoopTests)
----------------------------------------------------------------------
Traceback (most recent call last):
  File "tests/test_asyncio_trollius.py", line 61, in test
    raise Return(res)
StopIteration: 42

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "tests/test_asyncio_trollius.py", line 64, in test_asyncio_coroutine
    self.loop.run_until_complete(fut)
  File "/python-greenio-0.6.0/greenio/__init__.py", line 129, in run_until_complete
    return self._green_run(ovr, args, kwargs)
  File "/python-greenio-0.6.0/greenio/__init__.py", line 125, in _green_run
    return _LoopGreenlet(method).switch(*args, **kwargs)
  File "/usr/lib/python3/dist-packages/trollius/base_events.py", line 273, in run_until_complete
    return future.result()
  File "/usr/lib/python3/dist-packages/trollius/futures.py", line 277, in result
    raise self._exception
  File "/usr/lib/python3/dist-packages/trollius/tasks.py", line 247, in _step
    result = coro.send(value)
RuntimeError: generator raised StopIteration

...

FAILED (errors=3)

Full build log:
https://reproducible.debian.net/rb-pkg/unstable/amd64/python-greenio.html

-- System Information:
Debian Release: stretch/sid
APT prefers unstable
APT policy: (500, 'unstable')
Architecture: amd64 (x86_64)