mypy_primer -p test.py --bisect --debug --old 'v1.15.0' says this is #18972

Simpler repro:

from typing import Callable, TypeVar

T = TypeVar("T")


def foo(f: Callable[[], T]) -> T:
    ret = f()
    if ret is None:
        return ret
    return ret

I will take a look at this (hopefully during weekend). The best course of action may be to infer a type variable with upper bound None (or anything else that doesn't make a meaningful intersection with given type variable). Essentially we can do something like (very roughly) meet(T(bound=A), B) == T(bound=meet(A, B)).