anchor.diff:  
     @override
     List<FieldElement> get fields {
  -    if (_fields != null) {
  -      return _fields!;
  +    if (!identical(_fields, _Sentinel.fieldElement)) {
  +      return _fields;
       }
   
       if (linkedNode != null) {
         if (linkedNode is ExtensionDeclaration) {
           _createPropertiesAndAccessors();
  -        assert(_fields != null);
  -        return _fields!;
  +        return _fields;
         } else {
  -        return _fields = const [];
  -      }
  -    }
  -
  -    return _fields ?? const <FieldElement>[];
  +        return _fields;
  +      }
  +    }
  +
  +    return _fields;
     }
   
     set fields(List<FieldElement> fields) {
  
positive.code: 
    @override
    List<MethodElement> get methods {
      if (_methods == null) {
        if (linkedNode != null) {
          _resynthesizeMembers2();
        }
      }
      return _methods ?? const <MethodElement>[];
    }
  
    @override
  
negative.code: 
    @override
    List<FieldElement> get fields {
      if (!identical(_fields, _Sentinel.fieldElement)) {
        return _fields;
      }
  
      if (linkedNode != null) {
        if (linkedNode is ClassOrMixinDeclaration) {
          linkedContext!.applyResolution(linkedNode!);
          _createPropertiesAndAccessors();
          return _fields;
        } else {
          _fields = const [];
        }
      }
  
      return _fields;
    }
  
    @override
  