What’s more elegant

Optional<Header> resultcode = Arrays.stream(response.getAllHeaders())
         .filter(h -> "X-Header-Result".equals(h.getName()))
         .findFirst();
 
return resultcode.isPresent() ? resultcode.get().getValue() : "";

Or

String resultcode = Arrays.stream(response.getAllHeaders())
         .filter(h -> "X-Header-Result".equals(h.getName()))
         .findFirst().map(NameValuePair::getValue)
         .orElse("");
 
return resultcode;