PR #87 regenerated pb2 files using the latest version of grpcio-tools. There is an issue reported in #91 where the changes result in AttributeError: 'NoneType' object has no attribute 'message_types_by_name'. I was able to reproduce the issue in a virtual environment using the steps in #91. The issue is no longer present when I pin grpcio-tools<1.44.0 and regenerate protos using the previous version of grpcio-tools.

I've opened #93 to pin the version of grpcio-tools so development can continue in this repo.