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

sdk/lib/core/errors.dart

Index: sdk/lib/core/errors.dart
diff --git a/sdk/lib/core/errors.dart b/sdk/lib/core/errors.dart
index fec2de5295fb11943e74ca610d4eb28e3bbaac05..2425189a868a9c87d2894f5555b36b06573d7e46 100644
--- a/sdk/lib/core/errors.dart
+++ b/sdk/lib/core/errors.dart
@@ -154,7 +154,7 @@ class NoSuchMethodError implements Error {
         i++;
       });
     }
-    if (_existingArgumentNames === null) {
+    if (_existingArgumentNames == null) {
       return "NoSuchMethodError : method not found: '$_memberName'\n"
           "Receiver: ${safeToString(_receiver)}\n"
           "Arguments: [$sb]";
@@ -226,7 +226,7 @@ class UnsupportedError implements Error {
 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");
 }