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

runtime/lib/date_patch.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.
 // Dart core library.
 
 // VM implementation of _DateImpl.
 patch class _DateImpl {
   /* patch */ _DateImpl(int year,
                         int month,
                         int day,
                         int hour,
                         int minute,
                         int second,
                         int millisecond,
                         bool isUtc)
       : this.isUtc = isUtc,
         this.millisecondsSinceEpoch = _brokenDownDateToMillisecondsSinceEpoch(
             year, month, day, hour, minute, second, millisecond, isUtc) {
-    if (millisecondsSinceEpoch === null) throw new ArgumentError();
-    if (isUtc === null) throw new ArgumentError();
+    if (millisecondsSinceEpoch == null) throw new ArgumentError();
+    if (isUtc == null) throw new ArgumentError();
   }
 
   /* patch */ _DateImpl.now()
       : isUtc = false,
         millisecondsSinceEpoch = _getCurrentMs() {
   }
 
   /* patch */ String get timeZoneName {
     if (isUtc) return "UTC";
     return _timeZoneName(millisecondsSinceEpoch);
@@ skipping 284 matching lines @@
 
   static String _timeZoneNameForClampedSeconds(int secondsSinceEpoch)
       native "DateNatives_timeZoneName";
 
   static int _timeZoneOffsetInSecondsForClampedSeconds(int secondsSinceEpoch)
       native "DateNatives_timeZoneOffsetInSeconds";
 
   static int _localTimeZoneAdjustmentInSeconds()
       native "DateNatives_localTimeZoneAdjustmentInSeconds";
 }