Error initializing Union of Lists with an empty list

[elazarg]

The following test case

[case testUnionListInit]
from typing import Union, List
a = []  # type: Union[List[int], List[str]]
[builtins fixtures/list.pyi]

Results in

Expected:
Actual:
  main:2: error: Incompatible types in assignment (expression has type List[None], variable has type "Union[List[int], List[str]]") (diff)

This came up during PR #2154, but I think is an independent issue.

[elazarg]

Perhaps related to binder.py#L189?

[gvanrossum]

Doesn't sound like a very important issue, the example has questionable value. (I'm not saying it's not a bug -- just that I don't think it's urgent to fix it.)

[JukkaL]

Closing in favor of duplicate #6463 (the latter issue has a slight more interesting example).