#getInvalidValue only returns the element of a Set, if the element is the last element in the Path.

I have a use case, where user input is validated with the validator. The user is entering data in a single UI but the model behind the UI is rather complex with multiple classes with references between each other. One of these relations is a Set and without this patch, no visisble feedback can be given to the user which property exactly was invalid.

I understand your concerns about the specification conformity, espacially the javadoc on the Node interface. I think a special configuration option to activate the behaviour will be OK, I do not know how to implement that, though. Maybe someone else could implement that on top of my pull request?