IsEmptyConverter.cs

public class IsEmptyConverter : IValueConverter, IMarkupExtension
{
    public bool Inverted { get; set; }
    
    public object Convert(object value, Type targetType, object parameter, CultureInfo culture)
    {
        if(!(value is string stringValue)) return false;
 
        return Inverted ? !string.IsNullOrEmpty(stringValue) : string.IsNullOrEmpty(stringValue);
    }
    
    public object ConvertBack(object value, Type targetType, object parameter, CultureInfo culture)
    {
        return !(bool)Convert(value, targetType, parameter, culture);
    }
    
    public object ProvideValue(IServiceProvider serviceProvider)
    {
        return this;
    }
}