os.path.join() causes nonType error on prefect UI

[sivlElyh]

Hi, I am new to prefect. When I have a os.path.join(path, folder) in task, I can run flow from python script but not from prefect UI. path and folder are two strings
The error message is

Unexpected error: TypeError('expected str, bytes or os.PathLike object, not NoneType',)
Traceback (most recent call last):
File "c:\programdata\continuum\anaconda\envs\prefect_env\lib\site-packages\prefect\engine\runner.py", line 48, in inner
new_state = method(self, state, *args, **kwargs)
File "c:\programdata\continuum\anaconda\envs\prefect_env\lib\site-packages\prefect\engine\task_runner.py", line 860, in get_task_run_state
logger=self.logger,
File "c:\programdata\continuum\anaconda\envs\prefect_env\lib\site-packages\prefect\utilities\executors.py", line 298, in run_task_with_timeout
return task.run(*args, **kwargs) # type: ignore
File "C:/Users/yliyunhu/Workspace/prefect-fv/test_files/register_test.py", line 23, in say_hello
path = os.path.join(path, folder)
File "c:\programdata\continuum\anaconda\envs\prefect_env\lib\ntpath.py", line 76, in join
path = os.fspath(path)
TypeError: expected str, bytes or os.PathLike object, not NoneType

Has anyone run into the same error?

[kvnkho]

I have ideas, but I have a lot of follow-up questions and I sense this thread may get a bit long to diagnose what you are seeing. Could you join the Prefect Slack at prefect.io/slack and post a message there? Someone from the Prefect team will see it and help.

[sivlElyh]

thanks for advice