add custom_element package

pkg/mdv/lib/src/template_iterator.dart

 // Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 part of mdv;
 
 // This code is a port of Model-Driven-Views:
 // https://github.com/polymer-project/mdv
 // The code mostly comes from src/template_element.js
 
@@ skipping 141 matching lines @@
 bool _isSimpleBinding(List<String> tokens) =>
     tokens.length == 3 && tokens[0].isEmpty && tokens[2].isEmpty;
 
 /**
  * Parses {{ mustache }} bindings.
  *
  * Returns null if there are no matches. Otherwise returns
  * [TEXT, (PATH, TEXT)+] if there is at least one mustache.
  */
 List<String> _parseMustacheTokens(String s) {
-  if (s.isEmpty) return;
+  if (s.isEmpty) return null;
 
   var tokens = null;
   var length = s.length;
   var startIndex = 0, lastIndex = 0, endIndex = 0;
   while (lastIndex < length) {
     startIndex = s.indexOf('{{', lastIndex);
     endIndex = startIndex < 0 ? -1 : s.indexOf('}}', startIndex + 2);
 
     if (endIndex < 0) {
       if (tokens == null) return null;
@@ skipping 228 matching lines @@
         nodeExt._templateIterator = null;
       }
     }
 
     _nodeOrCustom(node).unbindAll();
     for (var c = node.firstChild; c != null; c = c.nextNode) {
       _unbindAllRecursively(c);
     }
   }
 }