Make Equality.hash accept null as an argument.

lib/src/equality.dart

 // Copyright (c) 2013, 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.
 
 import "dart:collection";
 
 import "comparators.dart";
 
 const int _HASH_MASK = 0x7fffffff;
 
@@ skipping 146 matching lines @@
     if (list1 == null || list2 == null) return false;
     int length = list1.length;
     if (length != list2.length) return false;
     for (int i = 0; i < length; i++) {
       if (!_elementEquality.equals(list1[i], list2[i])) return false;
     }
     return true;
   }
 
   int hash(List<E> list) {
-    if (elements == null) return null.hashCode;
+    if (list == null) return null.hashCode;
     // Jenkins's one-at-a-time hash function.
     // This code is almost identical to the one in IterableEquality, except
     // that it uses indexing instead of iterating to get the elements.
     int hash = 0;
     for (int i = 0; i < list.length; i++) {
       int c = _elementEquality.hash(list[i]);
       hash = (hash + c) & _HASH_MASK;
       hash = (hash + (hash << 10)) & _HASH_MASK;
       hash ^= (hash >> 6);
     }
@@ skipping 278 matching lines @@
 class CaseInsensitiveEquality implements Equality<String> {
   const CaseInsensitiveEquality();
 
   bool equals(String string1, String string2) =>
       equalsIgnoreAsciiCase(string1, string2);
 
   int hash(String string) => hashIgnoreAsciiCase(string);
 
   bool isValidKey(Object object) => object is String;
 }