prevent uncaught error when data.title is null

js/push.js

@@ -458,8 +458,7 @@
     }
 
     data.title = head.querySelector('title');
-    var text = 'innerText' in data.title ? 'innerText' : 'textContent';
-    data.title = data.title && data.title[text].trim();
+    data.title = data.title && data.title['innerText' in data.title ? 'innerText' : 'textContent'].trim();
 
     if (options.transition) {
       data = extendWithDom(data, '.content', body);