code: public static WriteFutureEx newNotWrittenFuture(IoSession session, Throwable cause) {
          DefaultWriteFutureEx unwrittenFuture = new DefaultWriteFutureEx(session);
          unwrittenFuture.setException(cause);
          return unwrittenFuture;
      }
docs: Returns a new {@link DefaultWriteFuture} which is already marked as 'not written'.