Null-safety

One of Kotlin’s key features is null-safety, which cleanly deals with null values at compile time rather than bumping into the famous NullPointerException at runtime. This makes applications safer through nullability declarations and expressing “value or no value” semantics without paying the cost of wrappers, such as Optional. Kotlin allows using functional constructs with nullable values. See this comprehensive guide to Kotlin null-safety.

Although Java does not let you express null-safety in its type-system, the Spring Framework provides null-safety of the whole Spring Framework API via tooling-friendly JSpecify annotations.

As of Kotlin 2.1, Kotlin enforces strict handling of nullability annotations from org.jspecify.annotations package.