None is not considered Hashable

[NeilGirdhar]

from typing import Hashable


def f() -> Hashable:
    return None


print(isinstance(None, Hashable))

The print returns True, so Python understands that None is hashable, but MyPy complains about incompatible return types:

error: Incompatible return value type (got "None", expected "Hashable")

[JukkaL]

Marking as high priority since typeshed is getting new Hashable type annotations, and these can cause false positives when updating to a more recent mypy release.