SQuAD-explorer | Visually Explore the Stanford Question Answering Dataset | Dataset library

You should simply treat them as invalid because you try to predict a proper answer span from the variable text. Everything else should be invalid. This is also the way how huggingface treats this predictions:

We could hypothetically create invalid predictions, e.g., predict that the start of the span is in the question. We throw out all invalid predictions.

You should also note that they use a more sopisticated method to get the predictions for each question (don't ask me why they show torch.argmax in their example). Please have a look at the example below: