(self, parameters)
return Union[arg, type(None)]
Optional type.

    Optional[X] is equivalent to Union[X, None].
Optional type.
Optional type .
def Optional(self, parameters):
    """Optional type.

    Optional[X] is equivalent to Union[X, None].
    """
    arg = _type_check(parameters, f"{self} requires a single type.")
    return Union[arg, type(None)]
def Optional ( self , parameters ) : arg = _type_check ( parameters , f"{self} requires a single type." ) return Union [ arg , type ( None ) ]