Buttons don't work on tutorial

Hi everyone, great tutorial but sometimes I get to the animal kingdom and the “done” button doesn’t do anything. I was able to get round it on the localhost version by signing in and out a bunch of times and with different browsers and eventually it just worked, but I don’t know why. Now I’m on the netlify version but I can’t get it to work. Is the done button supposed to be a link “kingdom/null” at the end? Null seems like a weird ending but I don’t know java so maybe I’m missing something