"None" has no attribute "foo"

[matthiaskramm]

Given

x = None
if x is not None:
  x.foo()

running mypy file.py reports:

file.py:3: error: "None" has no attribute "foo"

mypy version: mypy 0.570-dev-8ec7046787f92bf7b00d0c70f570fcb5d75e4b53

Passing --strict-optional makes the problem go away.

[bwo]

seems like this is related: #4520

[emmatyping]

I think this is in fact a duplicate of #4520, closing this as that issue has more discussion.