"multiple values for keyword argument" with star expansion

MyPy seems to be unaware of the length of a Tuple when wrapped in a Union:

from typing import Union, Tuple


def get_tuple() -> Union[Tuple[int, int], Tuple[None, None]]:
    return (1, 2)


def process_tuple(one, two, flag=False):
    print(one, two, flag)


process_tuple(*get_tuple(), flag=True)

1.py:12: error: "process_tuple" gets multiple values for keyword argument "flag"

Same code without a unionized type (def get_tuple() -> Tuple[int, int]:) works.

Start with the provided Python reproducer and trace mypy's handling of Union[Tuple[int, int], Tuple[None, None]] during star expansion and keyword checking. Done when the valid call no longer reports a duplicate flag argument and a regression test covers both the unionized and non-unionized cases.