This commit replaces `@Nonnull(when = When.MAYBE)` meta-annotation in
`org.springframework.lang.Nullable` by `@CheckForNull` in order to
prevent `unknown enum constant When.MAYBE` compilation warnings.
Closes gh-27183
Javadoc doesn't seem to like having `e.g.` as it thinks the sentence
ends there, which is usually incorrect and results in broken descriptions.
This commit rewords the doc strings slightly to avoid problematic parts.
Closes gh-32532
This commit introduces null-safety checks for spring-core at build-time
in order to validate the consistency of Spring null-safety annotations
and generate errors when inconsistencies are detected during a build
(similar to what is done with Checkstyle).
In order to make that possible, this commit also introduces a new
org.springframework.lang.Contract annotation inspired from
org.jetbrains.annotations.Contract, which allows to specify semantics
of methods like Assert#notNull in order to prevent artificial
additional null checks in Spring Framework code base.
This commit only checks org.springframework.core package, follow-up
commits will also extend the analysis to other modules, after related
null-safety refinements.
See gh-32475
Historically, we have rarely intentionally thrown a
NullPointerException in the Spring Framework. Instead, we prefer to
throw either an IllegalArgumentException or IllegalStateException
instead of a NullPointerException.
However, changes to the code in recent times have introduced the use of
Objects.requireNonNull(Object) which throws a NullPointerException
without an explicit error message.
The latter ends up providing less context than a NullPointerException
thrown by the JVM (since Java 14) due to actually de-referencing a
null-pointer. See https://openjdk.org/jeps/358.
In light of that, this commit revises our current use of
Objects.requireNonNull(Object) by removing it or replacing it with
Assert.notNull().
However, we still use Objects.requireNonNull(T, String) in a few places
where we are required to throw a NullPointerException in order to
comply with a third-party contract such as Reactive Streams.
Closes gh-32430
Sébastien Deleuze
Juergen Hoeller
Sam Brannen
Łukasz Jernaś
T45K
Stéphane Nicoll
Johnny Lim
Yanming Zhou