Fix mypy

    def __init__(self, argv: List[str], cwd: Optional[str] = None) -> None:

        self.argv = argv

        self.cwd = cwd or os.getcwd()

        self._database = None  # Do not assign default value: `None` means we don't know yet.

        self._database: Optional[str] = None  # Do not assign default value: `None` means we don't know yet.

    @property

    def database(self):