IsEmptyConverter.cs

public class IsEmptyConverter : IValueConverter
{

    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if(!(value is string stringValue)) return false;

        return string.IsNullOrEmpty(stringValue);
    }

    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return !(bool)Convert(value, targetType, parameter, culture);
    }

}