I saw DoAnswerStyleStubbing class code.
I thought that below is correct.

boolean isSet() {
    return !answers.isEmpty();
}

After execute setAnswers function with answers, instance will return isSet is false.
I think it looks strange.

And InvocationContainerImpl also need to be changed as follow.

public boolean hasAnswersForStubbing() {
    return doAnswerStyleStubbing.isSet();
}