Notice: Undefined index: cancel callback in uc_recurring_invoke()

When I cancel a subscription, I get this error:

Notice: Undefined index: cancel callback in uc_recurring_invoke() (line 732 of *****\sites\all\modules\contrib\uc_recurring\uc_recurring.module).

I think the code should be changed from

function uc_recurring_invoke($handler, $op, $params = array()) {
  $info = uc_recurring_get_recurring_info($handler);
  $function = $info[$op];
  if (function_exists($function)) {
    // Add the op argument to the params, in case the handler will need to use
    // it to identify the operation it is in.
    $params[] = $op;
    return call_user_func_array($function, $params);
  }
}

to

function uc_recurring_invoke($handler, $op, $params = array()) {
  $info = uc_recurring_get_recurring_info($handler);
  $function = isset($info[$op]) ? $info[$op] : "";
  if ($function && function_exists($function)) {
    // Add the op argument to the params, in case the handler will need to use
    // it to identify the operation it is in.
    $params[] = $op;
    return call_user_func_array($function, $params);
  }
}