public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
        {
            bool?booleanValue = ConverterHelper.GetNullableBooleanValue(value);

            if (targetType == typeof(bool))
            {
                return(booleanValue ?? false);
            }
            return(booleanValue);
        }
        public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
        {
            bool?booleanValue = ConverterHelper.GetNullableBooleanValue(value);

            if (booleanValue != null)
            {
                booleanValue = !booleanValue.Value;
            }
            if (targetType == typeof(bool))
            {
                return(booleanValue ?? true);
            }
            return(booleanValue);
        }