mypy should support optional tagged unions #8925

from typing import Literal, TypedDict, Union

class NewJob(TypedDict):
    event_type: Literal["new-job"]
    job_description: str

class CancelJob(TypedDict):
    event_type: Literal["cancel-job"]
    job_id: int

request: Union[NewJob, CancelJob, None]

# works
if request is not None:
    if request["event_type"] == "new-job":
        print("Starting new job", request["job_description"])

# fails with `main.py:20: error: TypedDict "CancelJob" has no key 'job_description'`
if request is not None and request["event_type"] == "new-job":
    print("Starting new job", request["job_description"])