PolymerExpressions: fix for null iterators in comprehensions

pkg/polymer_expressions/lib/eval.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.
 
 library polymer_expressions.eval;
 
 import 'dart:async';
 import 'dart:collection';
 import 'dart:mirrors';
 
@@ skipping 577 matching lines @@
 call(dynamic receiver, List args) {
   if (receiver is Method) {
     return
         _convert(receiver.mirror.invoke(receiver.symbol, args, null).reflectee);
   } else {
     return _convert(Function.apply(receiver, args, null));
   }
 }
 
 /**
- * A comprehension declaration ("a in b").
+ * A comprehension declaration ("a in b"). [identifier] is the loop variable
+ * that's added to the scope during iteration. [iterable] is the set of
+ * objects to iterate over.
  */
 class Comprehension {
   final String identifier;
   final Iterable iterable;
-  Comprehension(this.identifier, this.iterable);
+
+  Comprehension(this.identifier, Iterable iterable)
+      : iterable = (iterable != null) ? iterable : [];

[Jennifer Messerly, 2013/09/16 19:43:47]

const [] ?

[justinfagnani, 2013/09/16 20:02:57]

Done.

 }
 
 /**
  * A method on a model object in a [Scope].
  */
 class Method { //implements _FunctionWrapper {
   final InstanceMirror mirror;
   final Symbol symbol;
 
   Method(this.mirror, this.symbol);
 
   dynamic call(List args) => mirror.invoke(symbol, args, null).reflectee;
 }
 
 class EvalException implements Exception {
   final String message;
   EvalException(this.message);
   String toString() => "EvalException: $message";
 }