attrs: mypy/typing false positives

Using attrs 6e7b9f2 and mypy 0.720:

from typing import List, Dict, Any, Union, Optional
import attr


@attr.s
class Foo:
    # OK
    str_list: List[str] = attr.ib(
        validator=attr.validators.deep_iterable(
            attr.validators.instance_of(str), attr.validators.instance_of(list)
        )
    )
    # Incompatible types in assignment (expression has type "Optional[List[_T]]", variable has type "Optional[List[str]]")
    maybe_str_list: Optional[List[str]] = attr.ib(
        validator=attr.validators.optional(
            attr.validators.deep_iterable(
                attr.validators.instance_of(str), attr.validators.instance_of(list)
            )
        )
    )
    # OK
    str_dict: Dict[str, Any] = attr.ib(
        validator=attr.validators.deep_mapping(
            attr.validators.instance_of(str),
            attr.validators.instance_of(object),
            attr.validators.instance_of(dict),
        )
    )
    # OK
    maybe_str_dict: Optional[Dict[str, Any]] = attr.ib(
        validator=attr.validators.optional(
            attr.validators.deep_mapping(
                attr.validators.instance_of(str),
                attr.validators.instance_of(object),
                attr.validators.instance_of(dict),
            )
        )
    )
    # Argument 1 to "instance_of" has incompatible type "Tuple[Type[str], Type[int]]"; expected "Union[Tuple[Type[<nothing>], ...], Type[<nothing>]]"
    str_int: Union[str, int] = attr.ib(
        validator=attr.validators.instance_of((str, int))
    )
    # (the error is shown twice for some reason)
    # Argument 1 to "instance_of" has incompatible type "Tuple[Type[str], Type[int]]"; expected "Union[Tuple[Type[<nothing>], ...], Type[<nothing>]]"
    # Argument 1 to "instance_of" has incompatible type "Tuple[Type[str], Type[int]]"; expected "Union[Tuple[Type[None], ...], Type[None]]"
    maybe_str_int: Optional[Union[str, int]] = attr.ib(
        validator=attr.validators.optional(attr.validators.instance_of((str, int)))
    )

deep_iterable seems to have an issue when combined with optional, instance_of doesn’t like tuples of types.