WPF & Silverlight Visibility Converter

The following is a common WPF/Silverlight converter that converts either a text or boolean value into a System.Windows.Visibility value.

public class VisibilityConverter : IValueConverter
    {

        object IValueConverter.Convert(object value, System.Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            //test if is null
            if (value == null || value is DBNull)
            {
                throw new NullReferenceException("Visibility value contains a null value.");
            }
 
            //string type provided
            if (value.GetType() == typeof(string))
            {
                switch (value.ToString().ToLower())
                {
                    case "true":
                    case "yes":
                        return Visibility.Visible;
                    case "no":
                    case "false":
                        return Visibility.Collapsed;
                    default:
                        throw new ArgumentException(value + " is not a valid visibility value.");
                }
            }
 
            //boolean type provided
            if (value.GetType() == typeof(bool))
            {
                if ((bool)value)
                {
                    return Visibility.Visible;
                }
 
                return Visibility.Collapsed;
            }
 
            //numeric value provided
            int intValue;
            if (int.TryParse(value.ToString(), out intValue))
            {
                if (intValue == 0)
                {
                    return Visibility.Collapsed;
                }
 
                return Visibility.Visible;
            }
 
            //unknown type provided
            throw new ArgumentException("Unknown type supplied. Visibility value cannot be determined.");
        }
 
        object IValueConverter.ConvertBack(object value, System.Type targetType, object parameter, System.Globalization.CultureInfo culture)
        {
            throw new System.NotImplementedException();
        }
    }