I’ve been using a JSR-305 implementation (com.google.code.findbugs:jsr305 by Google) for framework-independent
nullness annotations, previously used in Guava, but that is now dormant for some time. Some people are using
Spotbugs, the sort-of successor to findbugs, others have opted for the
checker framework, while still others use whatever annotations happen to be made
available by the framework(s), libraries and IDEs they are using. It’s a bit of a mess.
It’s a good thing therefore that a bunch of people from Google, Jetbrains, Eclipse, Sonar, Facebook, Uber, Spring, SpotBugs, Checker Framework are working on a longer term solution, hopefully producing some initial version in the coming months.