Update List constructor documentation. Say that null is not a length.

sdk/lib/core/list.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.
 
 part of dart.core;
 
 /**
  * An indexable collection of objects with a length.
  *
  * Subclasses of this class implement different kinds of lists.
@@ skipping 42 matching lines @@
    *     fixedLengthList.length;     // 3
    *     fixedLengthList.length = 1; // Error
    *
    *
    * The list has length 0 and is growable if [length] is omitted.
    *
    *     List growableList = new List();
    *     growableList.length; // 0;
    *     growableList.length = 3;
    *
-   * An error occurs if [length] is negative.
+   * The [length] must not be negative or null, if it is provided.

[ngeoffray, 2013/10/29 12:13:50]

-> Throws an [ArgumentError] if [length] is provided and it is negative or null.

[Lasse Reichstein Nielsen, 2013/10/29 12:18:51]

I'd rather not say how it fails. It will most likely be an argument error. For
negative values, it could be a range error, or it might not.

    */
   external factory List([int length]);
 
   /**
    * Creates a fixed-length list of the given length, and initializes the
    * value at each position with [fill]:
    *
    *     new List<int>.filled(3, 0); // [0, 0, 0]
+   *
+   * The [length] must not be negative or null.

[ngeoffray, 2013/10/29 12:13:50]

-> Throws an [ArgumentError] if [length] is negative or null.

    */
   external factory List.filled(int length, E fill);
 
   /**
    * Creates a list and initializes it using the contents of [other].
    *
    * The [Iterator] of [other] provides the order of the objects.
    *
    * This constructor returns a growable list if [growable] is true;
    * otherwise, it returns a fixed-length list.
@@ skipping 354 matching lines @@
    * as values. The `Map.keys` [Iterable] iterates the indices of this list
    * in numerical order.
    *
    *     List<String> words = ['fee', 'fi', 'fo', 'fum'];
    *     Map<int, String> map = words.asMap();
    *     map[0] + map[1];   // 'feefi';
    *     map.keys.toList(); // [0, 1, 2, 3]
    */
   Map<int, E> asMap();
 }