Add JSpecify nullability annotations to the codebase.

Loose ends:

  • [x] #46776
  • [x] https://github.com/spring-projects/spring-boot/issues/46593
  • [x] Remove nullAwayVersion and errorProneVersion gradle properties after https://github.com/spring-gradle-plugins/nullability-plugin/issues/5 and https://github.com/spring-gradle-plugins/nullability-plugin/issues/4 is resolved and we're using 0.0.3 of the plugin
  • [x] Add ArchUnit / Checkstyle rule to verify that all packages are @NullMarked
  • [x] Review org.springframework.boot.jpa.EntityManagerFactoryBuilder.Builder#setPackagesToScan

Comment From: Nivetha217

Hi, I am interested to work on this issue. Could you please assign it to me?

Comment From: wilkinsona

Thanks for the offer, @Nivetha217, but this issue is already assigned to someone.

Comment From: Nivetha217

Thanks for letting me know. I will pick something else then.