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

sdk/lib/core/errors.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.
 
 class Error {
   const Error();
 }
 
 /**
  * Error thrown by the runtime system when an assert statement fails.
@@ skipping 136 matching lines @@
       _namedArguments.forEach((String key, var value) {
         if (i > 0) {
           sb.add(", ");
         }
         sb.add(key);
         sb.add(": ");
         sb.add(safeToString(value));
         i++;
       });
     }
-    if (_existingArgumentNames === null) {
+    if (_existingArgumentNames == null) {
       return "NoSuchMethodError : method not found: '$_memberName'\n"
           "Receiver: ${safeToString(_receiver)}\n"
           "Arguments: [$sb]";
     } else {
       String actualParameters = sb.toString();
       sb = new StringBuffer();
       for (int i = 0; i < _existingArgumentNames.length; i++) {
         if (i > 0) {
           sb.add(", ");
         }
@@ skipping 51 matching lines @@
  * If a class is not intending to implement the feature, it should throw
  * an [UnsupportedError] instead. This error is only intended for
  * use during development.
  *
  * This class temporarily implements [Exception] for backwards compatibility.
  * The constructor is temporarily const to support [NotImplementedException].
  */
 class UnimplementedError implements UnsupportedError, NotImplementedException {
   final String message;
   const UnimplementedError([String this.message]);
-  String toString() => (this.message !== null
+  String toString() => (this.message != null
                         ? "UnimplementedError: $message"
                         : "UnimplementedError");
 }
 
 
 /** Temporary class added for backwards compatibility. Will be removed. */
 interface NotImplementedException extends Exception default UnimplementedError {
   const NotImplementedException([String message]);
 }
 
@@ skipping 13 matching lines @@
 
 class OutOfMemoryError implements Error {
   const OutOfMemoryError();
   String toString() => "Out of Memory";
 }
 
 class StackOverflowError implements Error {
   const StackOverflowError();
   String toString() => "Stack Overflow";
 }