Use strict equality when comparing with null, especially when null is a default value.

corelib/src/implementation/splay_tree.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.
 
 /**
  * A node in a splay tree. It holds the key, the value and the left
  * and right children in the tree.
  */
 class SplayTreeNode<K, V> {
   SplayTreeNode(K k, V v) {
@@ skipping 163 matching lines @@
 
   bool isEmpty() {
     // assert(!((_root === null) && (_count != 0)));
     // assert(!((_count == 0) && (_root !== null)));
     return (_root === null);
   }
 
   void forEach(void f(K key, V value)) {
     List<SplayTreeNode<K, V>> list = new List<SplayTreeNode<K, V>>();
     SplayTreeNode<K, V> current = _root;
-    while (current != null) {
-      if (current.left != null) {
+    while (current !== null) {
+      if (current.left !== null) {
         list.add(current);
         current = current.left;
       } else {
         f(current.key, current.value);
-        while (current.right == null) {
+        while (current.right === null) {
           if (list.isEmpty()) return;
           current = list.removeLast();
           f(current.key, current.value);
         }
         current = current.right;
       }
     }
   }
 
   int get length() {
@@ skipping 27 matching lines @@
     forEach((K k, V v) { list.add(k); });
     return list;
   }
 
   Collection<V> getValues() {
     List<V> list = new List<V>();
     forEach((K k, V v) { list.add(v); });
     return list;
   }
 }