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

samples/swarm/swarm_ui_lib/util/StringUtils.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.
 
 /**
  * General purpose string manipulation utilities.
  */
 class StringUtils {
   /**
    * Returns either [str], or if [str] is null, the value of [defaultStr].
    */
   static String defaultString(String str, [String defaultStr='']) {
-    return str === null ? defaultStr : str;
+    return str == null ? defaultStr : str;
   }
 
   /** Parse string to a double, and handle null intelligently */
   static double parseDouble(String str, [double ifNull = null]) {
     return (str == null) ? ifNull : double.parse(str);
   }
 
   /** Parse string to a int, and handle null intelligently */
   static int parseInt(String str, [int ifNull = null]) {
     return (str == null) ? ifNull : int.parse(str);
   }
 
   /** Parse bool to a double, and handle null intelligently */
   // TODO(jacobr): corelib should have a boolean parsing method
   static bool parseBool(String str, [bool ifNull = null]) {
     assert(str == null || str == 'true' || str == 'false');
     return (str == null) ? ifNull : (str == 'true');
   }
 }