PolymerExpressions: fix for null iterators in comprehensions

pkg/polymer_expressions/test/syntax_test.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:async';
 import 'dart:html';
 
 import 'package:polymer_expressions/polymer_expressions.dart';
 import 'package:unittest/unittest.dart';
 import 'package:unittest/html_enhanced_config.dart';
 import 'package:observe/observe.dart';
 import 'package:mdv/mdv.dart' as mdv;
 
 main() {
   mdv.initialize();
   useHtmlEnhancedConfiguration();
 
-  group('syntax', () {
+  group('PolymerExpressions', () {
+    var testDiv;
+
     setUp(() {
-      document.body.nodes.add(new Element.html('''
+      document.body.append(testDiv = new DivElement());
+    });
+
+    tearDown(() {
+      testDiv.remove();
+      testDiv = null;
+    });
+
+    test('should make two-way bindings to inputs', () {
+      testDiv.nodes.add(new Element.html('''
           <template id="test" bind>
             <input id="input" value="{{ firstName }}">
           </template>'''));
-    });
-
-    tearDown(() {
-      query('#test')..unbindAll()..remove();
-    });
-
-    test('should make two-way bindings to inputs', () {
       var person = new Person('John', 'Messerly', ['A', 'B', 'C']);
       query('#test')
           ..bindingDelegate = new PolymerExpressions()
           ..model = person;
       return new Future.delayed(new Duration()).then((_) {
         InputElement input = query('#input');
         expect(input.value, 'John');
         input.focus();
         input.value = 'Justin';
         input.blur();
         var event = new Event('change');
         // TODO(justin): figure out how to trigger keyboard events to test
         // two-way bindings
       });
     });
 
+    test('should handle null collections in "in" expressions', () {
+      testDiv.nodes.add(new Element.html('''
+          <template id="test" bind>
+            <template repeat="{{ item in items }}">
+              {{ item }}
+            </template>
+          </template>'''));      
+      query('#test')
+          ..bindingDelegate = new PolymerExpressions(globals: {'items': null})
+          ..model = null;
+      // the template should be the only node
+      expect(testDiv.nodes.length, 1);
+      expect(testDiv.nodes[0].id, 'test');
+    });
   });
 }
 
 class Person extends Object with ChangeNotifierMixin {
   static const _FIRST_NAME = const Symbol('firstName');
   static const _LAST_NAME = const Symbol('lastName');
   static const _ITEMS = const Symbol('items');
   static const _GET_FULL_NAME = const Symbol('getFullName');
 
   String _firstName;
@@ skipping 21 matching lines @@
   List<String> get items => _items;
 
   void set items(List<String> value) {
     _items = value;
     notifyChange(new PropertyChangeRecord(_ITEMS));
   }
 
   String toString() => "Person(firstName: $_firstName, lastName: $_lastName)";
 
 }