406 Status on Response when invoking setErrorResul

I am trying to create a simple Spring RestController that uses RxJava's Observable class to perform async processing. Here is my code:

@RestController
@RequestMapping("/users")
public class UserController {
   @Autowired
   private UserAsyncRepository repository;

   @RequestMapping(value="/{userName}", method=GET)
   public DeferredResult<ResponseEntity<User>> getByUserName(
      @PathVariable String userName) {
      final DeferredResult<ResponseEntity<User>> deferred = 
         new DeferredResult<ResponseEntity<User>>();
      repository
         .findByUserName(userName)    // returns Observable<User>
         .singleOrDefault(null)
         .timeout(1, TimeUnit.SECONDS)
         .subscribe(u -> {
              if(u == null) {
                 deferred.setErrorResult(ResponseEntity.notFound());
              } else {
                 deferred.setResult(ResponseEntity.ok(u));
              }
           }, t -> {
              deferred.setErrorResult(ResponseEntity.status(HttpStatus.INTERNAL_SERVER_ERROR));
           }
         );
      return deferred;
   }
}

When this method is invoked with a valid userName, I get the response I expect with status 200. When this method is invoked with an invalid userName, the response is 406 instead of 404, which is what I expect. Let me know if you have any idea as to why this is happening.

Thanks in advance for your help.

By passing an instance of an exception to the setErrorResult method of the DeferredResult class, I was able to get the 404 response as expected. Here is my exception class:

@ResponseStatus(HttpStatus.NOT_FOUND)
public class ResourceNotFoundException extends RuntimeException {
   private static final long serialVersionUID = 1L;

   public ResourceNotFoundException(String message) {
      super(message);
   }
}

The key is making sure you add the @ResponseStatus annotation to your custom exception class.

HTH.