title: Intercept @RequestHeader exception for missing header
body: <p>I have a method in controller with has parameter for example </p>
  
  <pre><code>@RequestMapping(value = "/{blabla}", method = RequestMethod.POST)
  @ResponseStatus(HttpStatus.CREATED)
  public void post(@RequestHeader("ETag") int etag)
  </code></pre>
  
  <p>If there is no ETag header in request - client gets 400 (BAD_REQUEST), which is not any informative.
  I need to somehow handle this exception and send my own exception to client (I use JSON for this purpose).
  I know that I can intercept exception via  @ExceptionHandler, but in that case all HTTP 400 requests will be handled, but I want that have missing ETag in headers.
  Any ideas?</p>