Steps to reproduce

This line:

contradicts with this line:

And I think that the update parameter can actually never be str, right?

Expected behaviour

No mypy issue for

dispatcher.add_handler(telegram.ext.CommandHandler('start', start_command_handler))

and

def start_command_handler(update: telegram.Update, context: telegram.ext.CallbackContext) -> None:

Actual behaviour

Argument 2 to "CommandHandler" has incompatible type "Callable[[Update, CallbackContext], None]"; expected "Callable[[Union[str, Update], CallbackContext], None]" 

Configuration

Operating System:

macOS 10.15.7 (19H15)

Version of Python, python-telegram-bot & dependencies:

$ python -m telegram

python-telegram-bot 13.1
certifi 2020.11.08
Python 3.9.0 (default, Nov 21 2020, 14:01:50) [Clang 12.0.0 (clang-1200.0.32.27)]

Logs

Insert logs here (if necessary)