I was about to create a PR adding more specific typing (axis=None → axis: int | None = None to axis parameters in most high-level functions, but I noticed that #3238 added named axes. This is not reflected in the corresponding docstrings (axis (None or int): …), nor in the aforementioned type hints – with the exception of ak_moment.
Complicating things further, the therein-used type AxisName accepts any Hashable, which includes None, so if one were to use that in its current form everywhere, functions that don't allow None would no longer show type errors.
I'm new to this library and even newer to the development side of it, but the above does seem like an unintentional inconsistency. I'd be happy to help with fixing once it is decided how to.