使用WPF数据绑定将NULL值显示为"NULL"的最简单方法是什么？

public class NullToStringConverter : IValueConverter
{
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value == null)
        {
            return "NULL";
        }
        return value;
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if (value == null)
        {
            return null;
        }
        return value;
    }
}

   <local:NullToStringConverter x:Key="nullToStringConverter" />
</Window.Resources>

<TextBlock Text="{Binding SomeProperty, Converter={StaticResource nullToStringConverter}}" />