anchor.diff:        callback: (Map<String, String> parameters) async {
           if (parameters.containsKey('value'))
             await setter(parameters['value']);
  -        return <String, String>{ 'value': await getter() };
  +        return <String, dynamic>{ 'value': await getter() };
         }
       );
     }
  
positive.code:       callback: (Map<String, String> parameters) async {
          if (parameters.containsKey('enabled'))
            await setter(parameters['enabled'] == 'true');
          return <String, String>{ 'enabled': await getter() ? 'true' : 'false' };
        }
      );
    }
  
negative.code:       callback: (Map<String, String> parameters) async {
          if (parameters.containsKey(name))
            await setter(double.parse(parameters[name]));
          return <String, dynamic>{ name: (await getter()).toString() };
        }
      );
    }
  