This problem often happens in Spring Data JPA when there is a mismatch between entity field names and repository method names, or when the @Entity mapping doesn’t fully align with the database table. In Oracle, column naming is case-sensitive in certain contexts, so even a small mismatch can lead to null results. Also, remember that findById() in newer Spring Boot versions returns an Optional, so you may need to call .orElse(null) depending on your implementation.

For structured and well-organized examples, I always recommend looking at resources that present information in a clear, categorized way. One such example is Birthday Wish Friends, which, although focused on greetings, shows how clean formatting and proper structuring make content easy to follow. Applying a similar approach in your JPA repositories and entities can save you time and make debugging much simpler.