Yes, I have. 
Here we only write data from server. When we send data to server, we have a check `if(pipeToData.lastModified) {
					headers["if-modified-since"] = pipeToData.lastModified;
				}
				if(pipeToData.etag) {
					headers["if-none-match"] = pipeToData.etag;
				}` 
so it is impossible to send undefined to server. We could send to server only one of these tags, but it is a valid scenario.