Since there's nothing online anywhere or searchable for this issue, I am going to post about it even if it's just for me one day when I inevitably encounter this issue again and go searching for an answer.

I encountered an issue while publishing a module. The problem appeared out of nowhere but remained consistently in place, refusing me the ability to publish once it reared its ugly head:

Internal Error: Invalid compiler output.
Object reference not set to an instance of an object.

There's a known issue where if you have large components (like images) in a module, those large resources get stored in temporal storage on your PC as a performance measure. Unfortunately, as such, it's not entirely impossible for those files to get deleted or corrupted by some automated process or accidental manual deletion.

You can identify if you're having this issue in two steps. First, check the error logs and see if you have the following line in your stack trace:

If you do, open up your ailing module in Service Studio and click on each of your images. If the details pane in the lower right of Service Studio does not change when you click on an image, that image is not there anymore or is corrupted. Delete it, replace it. Do this for all images in your module and attempt to publish. If you're still not good, check your resources in a similar way.

Final note: it's probably a better architectural practice anyway to store images and large resource files in separate modules that you publish less anyway. It's very rare that you would need versioning of either to the same degree you want versioning for your code, so it's probably better to just cut the coupling and move it on out.