ng-repeat get corrupted when iterating over a null

[trinarytree]

to reproduce:
put this into a controller

dart code

@NgController(
    selector: '[foo-controller]',
    publishAs: 'ctrl')
class FooController {
  var foos = [1, 2];
  void clickFoo() {
    foos = foos == null ? [1, 2] : null;
  }
}

template code

<div foo-controller>
    <button ng-click="ctrl.clickFoo()">click me</button>
    {{ctrl.foos}}
    <div ng-repeat="foo in ctrl.foos">
      i'm a foo
    </div>
</div>

when you click on "click me" repeatedly, it will make the list shown on the page grow by 2 every other time.

[chirayuk]

I'll take this one.