Closed Domain Question Answering which doesn't answer Questions

I've been exploring Closed Domain Question Answering Implementations which have been trained on SQuAD 2.0 dataset. Ideally, it should not answer questions which the context text corpus doesn't contain answers to. But while implementing such models using the Haystack repo or the FARM repo, I'm finding that it always answers these questions even when it shouldn't. Is there any implementation available that takes into account the fact that it shouldn't answer questions when it doesn't find a suitable answer.

References:

1. https://colab.research.google.com/github/deepset-ai/haystack/blob/update-tutorials/tutorials/Tutorial3_Basic_QA_Pipeline_without_Elasticsearch.ipynb#scrollTo=KS4nTwxIbRb6

2. https://github.com/deepset-ai/FARM

3. https://github.com/deepset-ai/haystack

4. https://huggingface.co/deepset/bert-large-uncased-whole-word-masking-squad2

5. https://colab.research.google.com/drive/1UrKlHlf68hD3wwQDTctx2cQs6FMUxLLH?usp=sharing#scrollTo=J4jxYsxaG77O