IllegalArgumentException expects a string.

runtime/lib/array.dart

 // Copyright (c) 2011, 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 ArrayFactory<T> {
   factory Array.from(Iterable<T> other) {
     GrowableObjectArray<T> array = new GrowableObjectArray<T>();
     for (final e in other) {
       array.add(e);
     }
@@ skipping 75 matching lines @@
     }
   }
 
   void _copyFromObjectArray(ObjectArray src,
                             int srcStart,
                             int dstStart,
                             int count)
       native "ObjectArray_copyFromObjectArray";
 
   void setRange(int start, int length, List<T> from, [int startFrom = 0]) {
-    if (length < 0) throw new IllegalArgumentException(length);
+    if (length < 0) {
+      throw new IllegalArgumentException("negative length $length");
+    }
     copyFrom(from, start, startFrom, count);
   }
 
   void removeRange(int start, int length) {
     throw const UnsupportedOperationException(
         "Cannot remove range of a non-extendable array");
   }
 
   void insertRange(int start, int length, [T initialValue = null]) {
     throw const NotImplementedException();
@@ skipping 214 matching lines @@
     if (!hasNext()) {
       throw const NoMoreElementsException();
     }
     return _array[_pos++];
   }
 
   final Array<T> _array;
   final int _length;  // Cache array length for faster access.
   int _pos;
 }