Undefined index: payment_details in commerce_payment_order_transaction_add_form_validate()

/**
 * Payment method callback: checkout form.
 */
function commerce_pay_in_person_submit_form($payment_method, $pane_values, $checkout_pane, $order) {
  return array(
    'instructions' => array(
      '#type' => 'item',
      '#markup' => check_markup($payment_method['settings']['instructions']['value'],
        $payment_method['settings']['instructions']['format']),
    ),
    'dummy' => array(
      '#type' => 'hidden',
      '#value' => 'dummy',
    ),
  );
}