Please just change something. Weird combination of dead code and inferred None

Feature

foo = None

def bar() -> str:
    global foo
    if foo is not None:
        print("Hello")
    else:
        foo = "bar"
        return "lol"

This program type-checks, even though it's obviously wrong. It's not a bug, it's a feature:

• Inferred type of foo is None, even though Optional[str] was intended.
• Because foo has type None, the if foo is not None: part is eliminated as dead code, and therefore the missing return isn't detected.
• After setting foo = "bar", reveal_type(foo) shows str. Perhaps the assignment should be an error?

Pitch

A friend submitted a PR like this and thought it was fine.

The payload names no files, tests, or entry points. Start by running the provided snippet through mypy and reviewing how inferred None, global reassignment, unreachable branches, and missing returns are handled. A maintainer decision on the intended semantics and regression coverage is needed before implementation can be scoped.