Revert 13878

lib/core/exceptions.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.
 
 // Exceptions are thrown either by the VM or from Dart code.
 
 /**
  * Interface implemented by all core library exceptions.
  * Defaults to an implementation that only carries a simple message.
  */
@@ skipping 96 matching lines @@
 
 class UnsupportedOperationException implements Exception {
   const UnsupportedOperationException(String this._message);
   String toString() => "UnsupportedOperationException: $_message";
   final String _message;
 }
 
 
 class NotImplementedException implements Exception {
   const NotImplementedException([String message]) : this._message = message;
-  String toString() => (this._message != null
+  String toString() => (this._message !== null
                         ? "NotImplementedException: $_message"
                         : "NotImplementedException");
   final String _message;
 }
 
 
 class IllegalJSRegExpException implements Exception {
   const IllegalJSRegExpException(String this._pattern, String this._errmsg);
   String toString() => "IllegalJSRegExpException: '$_pattern' '$_errmsg'";
   final String _pattern;
   final String _errmsg;
 }
 
 
 class IntegerDivisionByZeroException implements Exception {
   const IntegerDivisionByZeroException();
   String toString() => "IntegerDivisionByZeroException";
 }
 
 /**
  * Exception thrown when a runtime error occurs.
  */
 class RuntimeError implements Exception {
   final message;
   RuntimeError(this.message);
   String toString() => "RuntimeError: $message";
 }