presto-proxy/src/main/java/io/prestosql/proxy/ProxyResponseHandler.java/ProxyResponseHandler/ProxyResponse
class ProxyResponseHandler:        private ProxyResponse(ListMultimap<HeaderName, String> headers, byte[] body)
        {
            this.headers = requireNonNull(headers, "headers is null");
            this.body = requireNonNull(body, "body is null");
        }