I have a personal wiki instance hosted for that purpose. I collect knowlege in it, that I might need later and forget. Although I might not use dokuwiki, if I had so start the wiki again (would go to markdown).

The german wetter.com has that feature.

I think null safety is an important step into software security. I like any approaches in that direction. But personally, I would just use kotlin. Kotlin and Java are so good with Interoperability that the transition is quite smooth and easy. Furthermore you get a better and more modern programming language without decades of technical dept.