protected function isIn($key, $value) : bool
    {
        $data = explode(',', $value);
        if (is_array($data) && in_array((string) $this->param[$key], $data)) {
            return true;
        }

        $this->errors[$key.self::ERROR] = $this->convertToFieldName($key)." must be in the given list of values $value.";
        return false;
    }