Morning, T
Thank you very much for pointing that out. I was astonished to read your post, because I couldn't believe null would be a non-presence in our word list, but I couldn't see how you could be mistaken about it.
It turns out that you've discovered a bug in our database. (Where are those spiders when we need 'em?) Apart from its general uses, null is also commonly used in computer programming circles to signify an absence of data. When I look in our word table, the entry after nuking looks something like this: In other words, nothing there. Obviously when the data was loaded, the instruction to insert 'null' was interpreted as meaning insert no value.
So, skipping over the technicalities, the result is that, although null is sort-of present in our word list, it's more or less invisible - null by name and null by nature. As it turns out, there doesn't seem to have been a daily puzzle until now where this would be an issue, although it has cropped up in a few random ones.
It's not practical for me to fix this up for today's puzzle, but I will fix things so it's not an issue in the future.
Thanks again for alerting me to this, T, and good luck with the rest of the puzzle.