Java 17: NPE when using Optional in Spring @Controller with Lombok
I'm encountering a `NullPointerException` when trying to return a response from a Spring `@Controller` method that uses `Optional` as a return type. My setup involves Java 17, Spring Boot 2.5, and Lombok for reducing boilerplate code. The controller method is intended to fetch a user by ID and return an `Optional<User>`. However, I get an exception when the user is not found, which seems to occur during serialization of the response. Here's a simplified version of my code: ```java @RestController @RequiredArgsConstructor public class UserController { private final UserService userService; @GetMapping("/users/{id}") public ResponseEntity<Optional<User>> getUserById(@PathVariable Long id) { return ResponseEntity.ok(userService.findById(id)); } } ``` And in my `UserService`: ```java @Service @RequiredArgsConstructor public class UserService { private final UserRepository userRepository; public Optional<User> findById(Long id) { return userRepository.findById(id); } } ``` The `UserRepository` is a standard Spring Data JPA repository. When I call this endpoint with an ID that does not exist, I see a `NullPointerException` in my logs, particularly during the serialization phase. The stack trace indicates that it happens while trying to convert the `Optional` to JSON, specifically in the `MappingJackson2HttpMessageConverter`. I expected that returning an empty `Optional` would yield a 204 No Content response, but instead, I get a 500 Internal Server Error. I also tried changing the return type to `ResponseEntity<User>` and handling the absence of a user myself, using `Optional.orElse(null)`, but that led to a different issue where the response structure was not as clean as I'd like. Has anyone faced a similar issue, and is there a recommended approach to handling `Optional` return types in Spring controllers without encountering a NPE?