Fixing Node.nodes.first.

tools/dom/templates/html/impl/impl_Node.darttemplate

 // 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 $LIBRARYNAME;
 
 /**
  * Lazy implementation of the child nodes of an element that does not request
  * the actual child nodes of an element until strictly necessary greatly
  * improving performance for the typical cases where it is not required.
  */
 class _ChildNodeListLazy implements List {
   final Node _this;
 
   _ChildNodeListLazy(this._this);
 
 
 $if DART2JS
   Node get first {
-    Node result = JS('Node', '#.firstChild', _this);
+    Node result = JS('Node|Null', '#.firstChild', _this);
     if (result == null) throw new StateError("No elements");
     return result;
   }
   Node get last {
-    Node result = JS('Node', '#.lastChild', _this);
+    Node result = JS('Node|Null', '#.lastChild', _this);
     if (result == null) throw new StateError("No elements");
     return result;
   }
   Node get single {
     int l = this.length;
     if (l == 0) throw new StateError("No elements");
     if (l > 1) throw new StateError("More than one element");
-    return JS('Node', '#.firstChild', _this);
+    return JS('Node|Null', '#.firstChild', _this);
   }
 $else
   Node get first {
     Node result = _this.$dom_firstChild;
     if (result == null) throw new StateError("No elements");
     return result;
   }
   Node get last {
     Node result = _this.$dom_lastChild;
     if (result == null) throw new StateError("No elements");
@@ skipping 270 matching lines @@
       }
     } else {
       for (var node in newNodes) {
         this.insertBefore(node, refChild);
       }
     }
   }
 
 $!MEMBERS
 }