Running MobAttacks.createDialog() gives me this:

This can be completely solved with some optional chaining. You can verify that by tricking it with something like this:
canvas.tokens = { controlled: [], objects: { children: [] }, releaseAll: () => {}, placeables: [] };
Running

MobAttacks.createDialog()gives me this:This can be completely solved with some optional chaining. You can verify that by tricking it with something like this: