anchor.diff:        } else {
           _mode = _MODE_IDENTITY_;
         }
  -    } else {
  -      if (obj is Map) {
  -        _mode =  _MODE_MAP_FIELD_;
  -        _instanceMirror = null;
  -      } else if (_getter != null) {
  -        _mode = _MODE_GETTER_;
  -        _instanceMirror = null;
  -      } else {
  -        _mode = _MODE_REFLECT_;
  -        _instanceMirror = reflect(obj);
  -      }
  +
  +      return;
  +    }
  +
  +    if (obj is Map) {
  +      _mode =  _MODE_MAP_FIELD_;
  +      _instanceMirror = null;
  +    } else if (_getter != null) {
  +      _mode = _MODE_GETTER_;
  +      _instanceMirror = null;
  +    } else {
  +      _mode = _MODE_REFLECT_;
  +      _instanceMirror = reflect(obj);
       }
     }
   
  
positive.code:     _object = obj;
      if (obj == null) {
        _mode = _MODE_IDENTITY_;
      } else if (field == null) {
        _instanceMirror = null;
        if (obj is Map) {
          if (_mode != _MODE_MAP_) {
  
negative.code:     identical(_iterable, collection)) {
        // Short circuit and assume that the list has not been modified.
        return false;
      }
  
      if (collection is List) {
        List list = collection;
        for(int index = 0; index < list.length; index++) {
          var item = list[index];
  