Custom Exception handling giving error Servlet.service() for servlet [dispatcherServlet]

Question

I have created a custom exception handling. I thought I have made it worked because it shows the error page on localhost and it's giving the correct info when I used the postman. However, on my terminal it's giving me this error -> Servlet.service() for servlet [dispatcherServlet] in context with path [] threw exception [Request processing failed; nested exception is org.springframework.web.client.HttpClientErrorException$Conflict: 409 null] with root cause.

Any suggestions on how to resolve this? Thanks

(Please note that I have a Rest Controller class and Web controller classes.)

@ControllerAdvice
public class CustomExceptionHandler extends ResponseEntityExceptionHandler {

    @ExceptionHandler(value = MyDuplicateEntryException.class)
    public ResponseEntity<MyErrorResponse> conflictErrorHandler(MyDuplicateEntryException e) throws IOException {
        return new ResponseEntity<>(new MyErrorResponse(e.getMessage()), CONFLICT);
    }
}


@ResponseStatus(CONFLICT)
public class MyDuplicateEntryException extends RuntimeException {

    public MyDuplicateEntryException(String errorMessage) {
        super(errorMessage);
    }
}

On ServiceImpl:
@Override
    public ResponseEntity<Artist> createArtist(AddArtistForm addArtistForm) throws DuplicateEntryException {

        String artistName = addArtistForm.getName();
        Optional<Artist> artist = artistRepository.findArtistByName(artistName);

        artist.ifPresent(a -> {
            throw new DuplicateEntryException(artist.get().getName() + " already exists");
        });

        return new ResponseEntity<>(artistRepository.save(new Artist(artistName)), CREATED);
    }