4c7735016b
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
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