Frog has hardwired access to NullPointerException: default argument can only be null.

corelib/src/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.
  */
 interface Exception default ExceptionImplementation {
@@ skipping 103 matching lines @@
 }
 
 
 class WrongArgumentCountException implements Exception {
   const WrongArgumentCountException();
   String toString() => "WrongArgumentCountException";
 }
 
 
 class NullPointerException implements Exception {
-  const NullPointerException([this.functionName,
-                              this.arguments = const[]]);
+  const NullPointerException([this.functionName, this.arguments]);
   String toString() {
     StringBuffer sb = new StringBuffer();
-    for (var arg in arguments) {
-      if (!sb.isEmpty()) sb.add(", ");
-      sb.add(arg);
+    if (arguments != null) {
+      for (var arg in arguments) {
+        if (!sb.isEmpty()) sb.add(", ");
+        sb.add(arg);
+      }
     }
     if (functionName == null) {
       return exceptionName;
     } else {
       return "$exceptionName : method: '$functionName'\n"
           "Receiver: null\n"
           "Arguments: [$sb]";
     }
   }
   
@@ skipping 34 matching lines @@
   String toString() => "IllegalJSRegExpException: '$_pattern' '$_errmsg'";
   final String _pattern;
   final String _errmsg;
 }
 
 
 class IntegerDivisionByZeroException implements Exception {
   const IntegerDivisionByZeroException();
   String toString() => "IntegerDivisionByZeroException";
 }