[Feature request] Port SQuAD 2.0 support
Recently the Google team added support for Squad 2.0:

https://github.com/google-research/bert/commit/60454702590a6c69bd45c5d4258c7e17b8a3e1da

Would be great to also have it available in the Pytorch version.
Hi, I don't have plan for that in the near future but feel free to open a PR.