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

sdk/lib/_internal/compiler/implementation/compile_time_constants.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.
 
 part of dart2js;
 
 /**
  * The [ConstantHandler] keeps track of compile-time constants,
  * initializations of global and static fields, and default values of
  * optional parameters.
@@ skipping 787 matching lines @@
       assignArgumentsToParameters(arguments);
       evaluateConstructorInitializers();
     });
   }
 
   List<Constant> buildJsNewArguments(ClassElement classElement) {
     List<Constant> jsNewArguments = <Constant>[];
     classElement.implementation.forEachInstanceField(
         (ClassElement enclosing, Element field) {
           Constant fieldValue = fieldValues[field];
-          if (fieldValue === null) {
+          if (fieldValue == null) {
             // Use the default value.
             fieldValue = compiler.compileConstant(field);
           }
           jsNewArguments.add(fieldValue);
         },
         includeBackendMembers: true,
         includeSuperMembers: true);
     return jsNewArguments;
   }
 }