code: public static HttpHandler getNext(HttpServerExchange httpServerExchange) {
  		String chainId = httpServerExchange.getAttachment(CHAIN_ID);
  		List<HttpHandler> handlersForId = handlerListById.get(chainId);
  		Integer nextIndex = httpServerExchange.getAttachment(CHAIN_SEQ);
  		// Check if we've reached the end of the chain.
  		if (nextIndex < handlersForId.size()) {
  			httpServerExchange.putAttachment(CHAIN_SEQ, nextIndex + 1);
  			return handlersForId.get(nextIndex);
  		}
  		return null;
  	}
docs: Returns the instance of the next handler, rather then calling handleRequest
  on it.
  
  @param httpServerExchange
  The current requests server exchange.
  @return The HttpHandler that should be executed next.