17.1.0 apparently breaks asdict

[pauloalem]

Hello there!
I have upgraded to 17.1.0 and aparently it breaks down on asdict convertion.
I've got this utility validator optional_instance_of that ends up raising a

return hash(_attrs_to_tuple(self, attrs))
TypeError: unhashable type: '_OptionalValidator'

Here's a sample to trigger that behavior:

import attr


def optional_instance_of(of):
    return attr.validators.optional(attr.validators.instance_of(of))


@attr.s()
class A:
    a = attr.ib(default=None, validator=optional_instance_of(int))

a = A()
print(attr.asdict(a, filter=attr.filters.exclude(type(None))))

Is this related to #142 ?

[hynek]

should be fixed by #193