/// <summary>
/// Get the target's null value from the current resource using the given key
/// </summary>
/// <param name="targetNullKey"></param>
/// <returns></returns>
private object GetTargetNullValue(Localize instance)
{
object value = GetValue(instance, instance.NullKey);
return((value is String) ? FormatCase(value as String, instance.CaseFormat) : value);
}