docs: public static void sendContinueResponseBlocking(final HttpServerExchange exchange) throws IOException {
          if (!exchange.isResponseChannelAvailable()) {
              throw UndertowMessages.MESSAGES.cannotSendContinueResponse();
          }
          if(exchange.getAttachment(ALREADY_SENT) != null) {
              return;
          }
          HttpServerExchange newExchange = exchange.getConnection().sendOutOfBandResponse(exchange);
          exchange.putAttachment(ALREADY_SENT, true);
          newExchange.setStatusCode(StatusCodes.CONTINUE);
          newExchange.getResponseHeaders().put(Headers.CONTENT_LENGTH, 0);
          newExchange.startBlocking();
          newExchange.getOutputStream().close();
          newExchange.getInputStream().close();
      }