One other thing that NullModule was commonly used for, is attaching custom Javascript to the page. Since NullModule didn't do anything, it was easy to tack your own custom methods on it and use it for custom requirements. However it was very finicky how you would attach the script and in that aspect it's really superceded by the Sideview CustomBehavior module, which makes the same basic idea much more resilient and easier to deal with.
Yep. NullModule is not a Sideview module. NullModule is just a flavorless module that does nothing besides exist. Sometimes you need a module just to be there, either to take up a spot for some advanced reason, or to act as the single common parent for a bunch of modules that it has downstream.
