Fixing Node.nodes.first.

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

Index: tools/dom/templates/html/impl/impl_Node.darttemplate
diff --git a/tools/dom/templates/html/impl/impl_Node.darttemplate b/tools/dom/templates/html/impl/impl_Node.darttemplate
index 94b84dce0724f6771333329de7325d0ad80ec3a8..018494ddb89ba8e50aa696314c3b2b2baec666fa 100644
--- a/tools/dom/templates/html/impl/impl_Node.darttemplate
+++ b/tools/dom/templates/html/impl/impl_Node.darttemplate
@@ -17,12 +17,12 @@ class _ChildNodeListLazy implements List {
 
 $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;
   }
@@ -30,7 +30,7 @@ $if DART2JS
     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 {