MyPy fail

main.py

#!/usr/bin/env python3

import mod


def do_the_thing():
    bar = mod.get_optional_bar()
    print(bar.x)

if __name__ == "__main__":
    do_the_thing()

mod.py

import random
from dataclasses import dataclass
from typing import Optional


@dataclass
class Bar:
    x: int

def get_optional_bar() -> Optional[Bar]:
    if random.randint(0, 1):
        return Bar(1)
    return None

output

$ mypy main.py
Success: no issues found in 1 source file