Use JavaScript logical NOT when parsing time

The jQuery isEmptyObject is not true on empty string.

issue11189
review356351002
(grafted from 1a7b8019712f02416507daa25761772eba125490)

--HG--
branch : 6.0

src/common.js

@@ -245,7 +245,7 @@
     };
 
     Sao.common.parse_time = function(format, value) {
-        if (jQuery.isEmptyObject(value)) {
+        if (!value) {
             return null;
         }
         var getNumber = function(pattern) {