public HttpRequestMessage build() {
        if (isBuilt) {
            throw new IllegalStateException("Builder must only be invoked once!");
        }
        isBuilt = true;
        return new HttpRequestMessageImpl(
                sessionContext, protocol, method, path, queryParams, headers, clientIp, scheme, port, serverName);
    }
Used to build a request with overridden values

@return `HttpRequestMessage`
zuul-core/src/main/java/com/netflix/zuul/message/util/HttpRequestBuilder.java