UnwrapError is not pickleable

[indigoviolet]

In [38]: pickle.loads(pickle.dumps(UnwrapError(Err(None), 'foo')))
---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
Cell In[38], line 1
----> 1 pickle.loads(pickle.dumps(UnwrapError(Err(None), 'foo')))

TypeError: UnwrapError.__init__() missing 1 required positional argument: 'message'

The reason this matters is that sometimes you want exceptions to come back over process boundaries, for ex. while using multiprocessing.