Use strict equality when comparing with null, especially when null is a default value.

corelib/src/implementation/promise_implementation.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.
 
 // Dart core library.
 
 class PromiseImpl<T> implements Promise<T> {
 
   // Enumeration of possible states:
   static final int CREATED = 0;
@@ skipping 143 matching lines @@
       _clearListeners();
       return true;
     }
     return false;
   }
 
   void addCompleteHandler(void completeHandler(T result)) {
     if (_state == COMPLETE_NORMAL) {
       completeHandler(_value);
     } else if (!isDone()) {
-      if (_normalListeners == null) {
+      if (_normalListeners === null) {
         _normalListeners = new Queue<Function>();
       }
       _normalListeners.addLast(completeHandler);
     }
   }
 
   void addErrorHandler(void errorHandler(err)) {
     if (_state == COMPLETE_ERROR) {
       errorHandler(_error);
     } else if (!isDone()) {
-      if (_errorListeners == null) {
+      if (_errorListeners === null) {
         _errorListeners = new Queue<Function>();
       }
       _errorListeners.addLast(errorHandler);
     }
   }
 
   void addCancelHandler(void cancelHandler()) {
     if (isCancelled()) {
       cancelHandler();
     } else if (!isDone()) {
-      if (_cancelListeners == null) {
+      if (_cancelListeners === null) {
         _cancelListeners = new Queue<Function>();
       }
       _cancelListeners.addLast(cancelHandler);
     }
   }
 
   // TODO(sigmund): consider adding to the API a method that does the following:
   // Promise chain(callback(T r)) {
   //   return then(callback).flatten();
   // }
@@ skipping 173 matching lines @@
         } 
       }
       return process(marshalled);
     }).flatten();
   }
 
   Promise<SendPort> _promise;
   static Map<SendPort, Dispatcher> _dispatchers;
 
 }