/// <summary>
 /// Performs a callback.  Null action and/or result are permitted.
 /// </summary>
 /// <param name="action">The optional callback action.</param>
 /// <param name="result">The result to pass back.</param>
 protected static void Callback(Action<ServiceResult> action, ServiceResult result)
 {
   if (action != null)
   {
     action(result);
   }
 }