Make undefined and null equivalent.

lib/compiler/implementation/emitter.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.
 
 /**
  * A function element that represents a closure call. The signature is copied
  * from the given element.
  */
 class ClosureInvocationElement extends FunctionElement {
   ClosureInvocationElement(SourceString name,
@@ skipping 306 matching lines @@
         int index = names.indexOf(element.name);
         if (index != -1) {
           indexOfLastOptionalArgumentInParameters = count;
           // The order of the named arguments is not the same as the
           // one in the real method (which is in Dart source order).
           argumentsBuffer[count] = jsName;
           parametersBuffer[selector.positionalArgumentCount + index] = jsName;
         } else {
           Constant value = handler.initialVariableValues[element];
           if (value == null) {
-            argumentsBuffer[count] = '(void 0)';
+            argumentsBuffer[count] = NullConstant.JsNull;
           } else {
             if (!value.isNull()) {
               // If the value is the null constant, we should not pass it
               // down to the native method.
               indexOfLastOptionalArgumentInParameters = count;
             }
             StringBuffer argumentBuffer = new StringBuffer();
             handler.writeConstant(argumentBuffer, value);
             argumentsBuffer[count] = argumentBuffer.toString();
           }
@@ skipping 691 matching lines @@
       mainBuffer.add('function init() {\n');
       mainBuffer.add('  $isolateProperties = {};\n');
       addDefineClassAndFinishClassFunctionsIfNecessary(mainBuffer);
       emitFinishIsolateConstructor(mainBuffer);
       mainBuffer.add('}\n');
       compiler.assembledCode = mainBuffer.toString();
     });
     return compiler.assembledCode;
   }
 }