Null-safe applications with Spring Boot 4 by Sébastien Deleuze @ Spring I/O 2026

This talk explores how to transform existing Spring Boot applications into null-safe ones, addressing the concept of "the billion dollar mistake" through the use of JSpecify annotations. The speaker guides the audience through the step-by-step process of making an application null-safe, highlighting the nullability features of popular IDEs and the role of AI-assisted development. Various examples of Spring APIs that utilize explicit nullability are discussed, along with guidance on configuring NullAway with Gradle or Maven for build-time null-safety checks. The session concludes with a look ahead, offering insights into future Java features that may support null-restricted types and how JSpecify can prepare codebases for these advancements.