Environment details

OS: OS X and Linux
Python 3.8.1rc1
google-cloud-pubsub==1.1.0
PubSub Emulator running out of the google/cloud-sdk:latest docker image

Steps to reproduce

I'm working on getting an isolated reproduction of this, but at current it's "run my integration tests against the PubSub emulator" (closed source, unfortunately) and see that on 1.1.0 the stack trace listed below gets written to stdout/stderr as it's seemingly occurring in another thread (not in my logs), and the test suite continues on normally and eventually passes. When pinned on 1.0.2, the stack trace below does not occur.

For whatever it's worth, our code using PubSub via a streaming pull future has not changed recently.

I get that this isn't very helpful by itself but I wanted to get report this sooner than later, instead of just pinning to 1.0.2 and forgetting about it.

Stack trace

ERROR:google.api_core.bidi:Thread-ConsumeBidirectionalStream caught unexpected exception 'NoneType' object has no attribute 'received_messages' and will exit.
Traceback (most recent call last):
  File "/Users/briancurtin/elastic/cloud/python-services-v3/.tox/integration/lib/python3.8/site-packages/google/api_core/bidi.py", line 657, in _thread_main
    self._on_response(response)
  File "/Users/briancurtin/elastic/cloud/python-services-v3/.tox/integration/lib/python3.8/site-packages/google/cloud/pubsub_v1/subscriber/_protocol/streaming_pull_manager.py", line 547, in _on_response
    len(response.received_messages),
AttributeError: 'NoneType' object has no attribute 'received_messages'