diff --git a/src/util.js b/src/util.js
index c2f30918d..7057ebb6b 100644
--- a/src/util.js
+++ b/src/util.js
@@ -85,6 +85,8 @@ function assert(cond, msg) {
 // Combines two URLs. The baseUrl shall be absolute URL. If the url is an
 // absolute URL, it will be returned as is.
 function combineUrl(baseUrl, url) {
+  if (!url)
+    return baseUrl;
   if (url.indexOf(':') >= 0)
     return url;
   if (url.charAt(0) == '/') {
diff --git a/test/unit/util_spec.js b/test/unit/util_spec.js
index c5743d6cc..d1f5a7387 100644
--- a/test/unit/util_spec.js
+++ b/test/unit/util_spec.js
@@ -45,6 +45,22 @@ describe('util', function() {
       var expected = 'http://server/test2.html';
       expect(result).toEqual(expected);
     });
+
+    it('returns base url when url is empty', function() {
+      var baseUrl = 'http://server/index.html';
+      var url = '';
+      var result = combineUrl(baseUrl, url);
+      var expected = 'http://server/index.html';
+      expect(result).toEqual(expected);
+    });
+
+    it('returns base url when url is undefined', function() {
+      var baseUrl = 'http://server/index.html';
+      var url;
+      var result = combineUrl(baseUrl, url);
+      var expected = 'http://server/index.html';
+      expect(result).toEqual(expected);
+    });
   });
 
 });