fix: skip handle empty url

Author: evilebottnawi

lib/urls.js

@@ -62,9 +62,9 @@ module.exports = function (css) {
 			.replace(/^'(.*)'$/, function(o, $1){ return $1; });
 
 		// already a full url? no change
-		if (/^(#|data:|http:\/\/|https:\/\/|file:\/\/\/)/i.test(unquotedOrigUrl)) {
-		  return fullMatch;
-		}
+    if (/^(#|data:|http:\/\/|https:\/\/|file:\/\/\/|\s*$)/i.test(unquotedOrigUrl)) {
+      return fullMatch;
+    }
 
 		// convert the url to a full url
 		var newUrl;

test/fixUrls.test.js

@@ -143,6 +143,17 @@ describe("fix urls tests", function() {
         assertUrl("body { background-image:url(#bg.jpg); }");
     });
 
+    // empty urls
+    it("Empty url should be skipped", function() {
+      assertUrl("body { background-image:url(); }");
+      assertUrl("body { background-image:url( ); }");
+      assertUrl("body { background-image:url(\n); }");
+      assertUrl("body { background-image:url(''); }");
+      assertUrl("body { background-image:url(' '); }");
+      assertUrl("body { background-image:url(\"\"); }");
+      assertUrl("body { background-image:url(\" \"); }");
+    });
+
     // rooted urls
     it("Rooted url", function() {
       assertUrl(