From f9be417204695d26d5f458fbc53870b2adb9a372 Mon Sep 17 00:00:00 2001
From: Bram Chen <bram.chen@gmail.com>
Date: Sat, 5 May 2018 18:40:41 +0800
Subject: [PATCH] Minor tweak for RetrieveETag (#3257)

Need to check if the server responses a null value for ETag.
(In the case testing with build-in webdav server of CarotDAV on Windows 10)
---
 core/modules/savers/put.js | 5 +++--
 1 file changed, 3 insertions(+), 2 deletions(-)

diff --git a/core/modules/savers/put.js b/core/modules/savers/put.js
index e1fd7a8c2..473025e2c 100644
--- a/core/modules/savers/put.js
+++ b/core/modules/savers/put.js
@@ -25,8 +25,9 @@ var RetrieveETag = function(self) {
 		type: "HEAD",
 		headers: headers,
 		callback: function(err, data, xhr) {
-			if(!err) {
-				self.etag = xhr.getResponseHeader("ETag").replace(/^W\//,"");
+			var etag = xhr.getResponseHeader("ETag");
+			if(!err && etag) {
+				self.etag = etag.replace(/^W\//,"");
 			}
 		}
 	});