Any seasoned Drupal developer has undoubtedly, at one point or another, come across the infamous "white screen of death" (WSOD) issue. While there are many documented (common) potential causes for this problem, today I encountered a new one, and just like all the ones before, it was a huge pain to find it!

In my case, the problem was that I had an implementation of hook_theme() that did not return any data. This caused my modules page to display the WSOD, and from there the whole site followed suit. Interestingly enough, there's a warning about this in the hook_theme() comments section, but who reads those things...