See:

• https://github.com/jspecify/jspecify
• https://spring.io/blog/2025/03/10/null-safety-in-spring-apps-with-jspecify-and-null-away
• Add nullability annotations and compile-time checks junit-team/junit-framework#4557
• Add JSpecify and NullAway scordio/jimfs-junit-jupiter#27
• https://github.com/uber/NullAway/wiki/Configuration#custom-contract-annotations

NullAway issues related to AssertJ:

• Feature request: Recognize common "assertThat(...).isNotNull()" statements uber/NullAway#301
• assertThat(...).as(...).isNotNull() is not recognized uber/NullAway#877
• assertThat(...).isNotNull() does not qualify null-check for collections uber/NullAway#1219
• AssertJ's fail* methods do not qualify as throw statements uber/NullAway#1222
• assertThat(...).hasSize(...) does not qualify null-check for collections uber/NullAway#1224

Deliverables

• Annotate AssertJ packages as @NullMarked
• Enable NullAway for build-time checks