private static void InvokeCallbackCommand( SelectContactInteraction selectContact, IList<Contact> contacts )
        {
            Contract.Requires( selectContact != null );
            Contract.Requires( contacts != null );

            if ( contacts.Any() )
            {
                // set contacts and execute accept
                selectContact.Contacts.ReplaceAll( contacts );
                selectContact.ExecuteDefaultCommand();
            }
            else
            {
                // execute cancel
                selectContact.ExecuteCancelCommand();
            }
        }