org.springframework.lang

## 注释类型 Nullable

-     @Target(value={METHOD,PARAMETER,FIELD})
       @Retention(value=RUNTIME)
       @Documented
       @Nonnull(when=MAYBE)
       @TypeQualifierNickname
      public @interface Nullable

  A common Spring annotation 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 Spring API.

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

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

  从以下版本开始:
    5.0
  作者:
    Sebastien Deleuze, Juergen Hoeller
  另请参阅:
    `NonNullApi`, `NonNullFields`, `NonNull`