Full traceback

Unexpected error: AttributeError("'NoneType' object has no attribute 'is_finished'")
Traceback (most recent call last):
  File "/usr/local/lib/python3.8/site-packages/prefect/engine/runner.py", line 48, in inner
    new_state = method(self, state, *args, **kwargs)
  File "/usr/local/lib/python3.8/site-packages/prefect/engine/task_runner.py", line 365, in check_upstream_finished
    if not all(s.is_finished() for s in all_states):
  File "/usr/local/lib/python3.8/site-packages/prefect/engine/task_runner.py", line 365, in <genexpr>
    if not all(s.is_finished() for s in all_states):
AttributeError: 'NoneType' object has no attribute 'is_finished'

Unexpected error: AttributeError("'NoneType' object has no attribute 'is_skipped'")
Traceback (most recent call last):
  File "/usr/local/lib/python3.8/site-packages/prefect/engine/runner.py", line 48, in inner
    new_state = method(self, state, *args, **kwargs)
  File "/usr/local/lib/python3.8/site-packages/prefect/engine/task_runner.py", line 401, in check_upstream_skipped
    if self.task.skip_on_upstream_skip and any(s.is_skipped() for s in all_states):
  File "/usr/local/lib/python3.8/site-packages/prefect/engine/task_runner.py", line 401, in <genexpr>
    if self.task.skip_on_upstream_skip and any(s.is_skipped() for s in all_states):
AttributeError: 'NoneType' object has no attribute 'is_skipped'

What is weird about this error is that it occurs in a mapped task run, when the rest of the mapped child tasks run successfully - also I thought this might have to do with our custom Result subclass - but caching works fine when re-running things... Also when re-running the same flow I face another strange error

Unexpected error: Exception("[Errno 2] No such file or directory: '/dask-worker-space/dask-worker-space/worker-wlwh86o0/storage/FeatureConstructorTask%3A%3Atest_task-3a38565741a24ddcac1e46f44f6fed21'")