AttributeError: 'Stdout' object has no attribute 'isatty' in vt100.py

Hit this error (trace below) running the Asynssh demo code from jonathanslenders. It was working so I don't know what happened.

Anyway, adding this to class Stdout in server.py seems to fix it, but I really don't know what I am doing.
def isatty(s):
return True

Perhaps someone who knows the code could take a look at it?

Traceback (most recent call last):
File "/mnt/pycode/ethametcli/venvcli/lib/python3.8/site-packages/prompt_toolkit/contrib/ssh/server.py", line 89, in _interact
await self.interact(self)
File "ethacli.py", line 65, in interact
prompt_session = PromptSession()
File "/mnt/pycode/ethametcli/venvcli/lib/python3.8/site-packages/prompt_toolkit/shortcuts/prompt.py", line 466, in init
self.app = self._create_application(editing_mode, erase_when_done)
File "/mnt/pycode/ethametcli/venvcli/lib/python3.8/site-packages/prompt_toolkit/shortcuts/prompt.py", line 717, in _create_application
application: Application[_T] = Application(
File "/mnt/pycode/ethametcli/venvcli/lib/python3.8/site-packages/prompt_toolkit/application/application.py", line 310, in init
self.renderer = Renderer(
File "/mnt/pycode/ethametcli/venvcli/lib/python3.8/site-packages/prompt_toolkit/renderer.py", line 362, in init
if not output.responds_to_cpr:
File "/mnt/pycode/ethametcli/venvcli/lib/python3.8/site-packages/prompt_toolkit/output/vt100.py", line 701, in responds_to_cpr
return self.stdout.isatty()
AttributeError: 'Stdout' object has no attribute 'isatty'

Start with the Stdout class in server.py and the responds_to_cpr property in vt100.py, following the traceback to understand the missing terminal capability. Reproduce the Asynssh demo failure and verify that the prompt session starts without the AttributeError, including the reported Stdout behavior.