Jackson 3 Is the Migration Inside Your Spring Boot 4 Migration
You migrated to Spring Boot 4. The app boots. Then a RestClient call starts blowing up on payloads that carry explicit nulls for primitive fields — even though your ObjectMapper config disables FAIL_ON_NULL_FOR_PRIMITIVES (your clients send those nulls; Jackson 2 let them through). You stare at the config bean. It’s right there. It’s also completely ignored — and Jackson 3 flips that feature to fail-by-default, so the new default silently takes over. ...