Item-Specificity Statistics

In your academic paper "Fine-Grained Spoiler Detection from Large-Scale Review Corpora" (ACL 2019) you plotted a statistic called DF-IIF that shows the importance of a word for a specific item.

I have two questions about it:

1. What are you doing in case of OOV token (let's say for sentences coming from the test set)?
2. Can you please share your code for that calculation as well?

Thanks.