Problem
With JSR-305 a proposal for "Annotations for Software Defect Detection" was published. The most prominent annotations were javax.annotation.Nullable and javax.annotation.Nonnull which are already supported in a lot of static code analysis tools and IDEs. Unfortunately JSR-305 never got included in official Java releases, and is currently in status "dormant". It's unlikely that the JCP process is ever taken up again. So the usage of the namespace javax.annotation is somewhat illegal. Last but not least it's very problematic to use them in Java 9 and up (see this article for details).
...