WPF / Silverlight Abstract Value Converter

using System.Windows.Data;
public abstract class BaseValueConverter<TFrom> : IValueConverter
{
    protected abstract object DoConversion(TFrom toConvert, object parameter);       
 
    #region IValueConverter Members
 
    public object Convert(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        if (!(value is TFrom))
            return DependencyProperty.UnsetValue;
 
        return DoConversion((TFrom)value, parameter);
    }
 
    public object ConvertBack(object value, Type targetType, object parameter, System.Globalization.CultureInfo culture)
    {
        throw new NotImplementedException();
    }
 
    #endregion
}