Extend null-safety to field level [SPR-15720]

[spring-projects-issues]

Juergen Hoeller opened SPR-15720 and commented

After the measures in #20099, we have consistent @Nullable declarations at the method parameter and return type level already. It turns out that @Nullable at the field level is an essential companion, avoiding mismatches between methods and the fields that they access.

Also, Eclipse only supports "full" nullability through annotations: that is, it doesn't differentiate between parameter level and field level. Extending our @NonNullApi / @Nullable semantics to the field level makes it easier to set those up for Eclipse as well.

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Affects: 5.0 RC2

Issue Links:

• Introduce null-safety of Spring Framework API [SPR-15540] #20099 Introduce null-safety of Spring Framework API
• ExceptionHandlerMethodResolver loses all handler methods [SPR-15907] #20461 ExceptionHandlerMethodResolver loses all handler methods
• Exporting a lazily initialized bean (which implements SelfNaming and is annotated with ManagedResource annotation) gives IllegalStateException [SPR-17592] #22124 Exporting a lazily initialized bean (which implements SelfNaming and is annotated with ManagedResource annotation) gives IllegalStateException
• org.apache.tomcat.websocket.WsSession.requestUri can be null [SPR-15721] #20277 org.apache.tomcat.websocket.WsSession.requestUri can be null
• JSP tags doesn't pick up JSTL-defined time zone at page level [SPR-15746] #20302 JSP tags doesn't pick up JSTL-defined time zone at page level
• SpEL : Indexed access within an expression with null variables is no longer a SpelEvaluationException [SPR-16544] #21087 SpEL : Indexed access within an expression with null variables is no longer a SpelEvaluationException
• Revisit nullability annotations towards GA [SPR-15756] #20311 Revisit nullability annotations towards GA
• Backport selected refinements from the nullability efforts in 5.0 [SPR-15656] #20215 Backport selected refinements from the nullability efforts in 5.0
• Make getters and setters null-safety consistent [SPR-15792] #20347 Make getters and setters null-safety consistent

Referenced from: commits 46eba3d, 9fc4fb1, 00f4c36, c292a89, 301e2ea, cc74a28, 57f961e