anchor.diff:  
     /// If `true`, then NNBD types are returned.
     /// If `false`, then legacy types are returned.
  -  final bool _isNonNullableByDefault;
  +  final bool isNonNullableByDefault;
   
     ClassElement _boolElement;
     ClassElement _doubleElement;
  
positive.code:   }
  
    @override
    DartObjectImpl get nullObject {
      if (_nullObject == null) {
        _nullObject = DartObjectImpl(nullType, NullState.NULL_STATE);
      }
      return _nullObject;
    }
  
    @override
    InterfaceType get nullType {
      _nullType ??= _getType(_coreLibrary, "Null");
      return _nullType;
  
negative.code: 
    @override
    DartType get bottomType {
      if (isNonNullableByDefault) {
        return NeverTypeImpl.instance;
      }
      return NeverTypeImpl.instanceLegacy;
  