8266 no processor (develop)

--rebased-from #2528

Rather than copy the workaround to the development branch, this PR solves the periodic "No processor" error by following the ZeroC suggestion of simply not passing string-ified proxies, which we couldn't do in 5.0 since it's a breaking change. Assuming the Python tests pass (especially `test_inputs.py`), then this should be good to go.