code: private static <T> BiConsumer<T, Throwable> completeHandler(CompletableCompletionStage<T> s) {
          return (result, failure) -> {
              if (failure == null) {
                  s.complete(result);
              } else {
                  handleFailure(s, failure);
              }
          };
      }
docs: Handler that can be used in whenComplete method.
  
  @return BiConsumer that passes values to this CompletionStage.