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

utils/apidoc/apidoc.dart

 // Copyright (c) 2012, 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.
 
 /**
  * This generates the reference documentation for the core libraries that come
  * with dart. It is built on top of dartdoc, which is a general-purpose library
  * for generating docs from any Dart code. This library extends that to include
  * additional information and styling specific to our standard library.
  *
@@ skipping 395 matching lines @@
   doc.DocComment getMemberComment(MemberMirror member) {
     return _mergeDocs(
         includeMdnMemberComment(member), super.getMemberComment(member),
         htmldoc.getRecordedMemberComment(member));
   }
 
   doc.DocComment _mergeDocs(MdnComment mdnComment,
                             doc.DocComment fileComment,
                             doc.DocComment handWrittenComment) {
     // Prefer the hand-written comment first.
-    if (handWrittenComment !== null) return handWrittenComment;
+    if (handWrittenComment != null) return handWrittenComment;
 
     // Otherwise, prefer comment from the (possibly generated) Dart file.
-    if (fileComment !== null) return fileComment;
+    if (fileComment != null) return fileComment;
 
     // Finally, fallback on MDN if available.
-    if (mdnComment !== null) {
+    if (mdnComment != null) {
       mdnUrl = mdnComment.mdnUrl;
       return mdnComment;
     }
 
     // We got nothing!
     return null;
   }
 
   void docType(TypeMirror type) {
     // Track whether we've inserted MDN content into this page.
@@ skipping 147 matching lines @@
    return '''
         <div class="mdn">
         $mdnComment
         <div class="mdn-note"><a href="$mdnUrl">from MDN</a></div>
         </div>
         ''';
   }
 
   String toString() => mdnComment;
 }