A common Reactor annotation (similar to Spring ones) to declare that annotated elements can be null under some circumstance. Leverages JSR 305 meta-annotations to indicate nullability in Java to common tools with JSR 305 support and used by Kotlin to infer nullability of Reactor API.

Should be used at parameter, return value, and field level. Methods overrides should repeat parent @Nullable annotations unless they behave differently.

Can be used in association with NonNullApi to override the default non-nullable semantic to nullable.