a === b -> identical(a, b)

samples/swarm/DataSource.dart

 // Copyright (c) 2011, 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.
 
 /** The top-level collection of all sections for a user. */
 // TODO(jimhug): This is known as UserData in the server model.
 class Sections implements Collection<Section> {
   final List<Section> _sections;
 
   Sections(this._sections);
@@ skipping 200 matching lines @@
     // By default images from the real server are cached.
     // Bump the version flag if you change the thumbnail size, and you want to
     // get the new images. Our server ignores the query params but it gets
     // around appengine server side caching and the client side cache.
     return 'data/$dataUri.jpg';
   }
 
   // TODO(jimhug): need to return a lazy Observable<String> and also
   //   add support for preloading.
   void _ensureLoaded() {
-    if (_htmlBody !== null) return;
+    if (_htmlBody != null) return;
 
     var name = '$dataUri.html';
     if (Sections.runningFromFile) {
       _htmlBody = CannedData.data[name];
     } else {
       // TODO(jimhug): Remove this truly evil synchronoush xhr.
       final req = new HttpRequest();
       req.open('GET', 'data/$name', false);
       req.send();
       _htmlBody = req.responseText;
     }
   }
 
   static Article decodeHeader(Feed source, Decoder decoder) {
     final id = decoder.readString();
     final title = decoder.readString();
     final srcUrl = decoder.readString();
     final hasThumbnail = decoder.readBool();
     final author = decoder.readString();
     final dateInSeconds = decoder.readInt();
     final snippet = decoder.readString();
     final date =
         new Date.fromMillisecondsSinceEpoch(dateInSeconds*1000, isUtc: true);
     return new Article(source, id, date, title, author, srcUrl, hasThumbnail,
         snippet);
   }
 }