Adding explicit spring.flyway.* config (url/user/password) ensures Flyway creates its own JDBC connection and runs migrations independently of the JPA datasource initialization order in Spring Boot 4.0. Fix DataInitializer creating a Document with title=null, which would hit the NOT NULL constraint in the documents table once the admin user init succeeds. Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>