atk4\data\Persistence::_serializeSaveField PHP Method

    public function _serializeSaveField(Field $f, $value)
    {
        switch ($f->serialize === true ? 'serialize' : $f->serialize) {
            case 'serialize':
                return serialize($value);
            case 'json':
                return json_encode($value);
            case 'base64':
                if (!is_string($value)) {
                    throw new Exception(['Field value can not be base64 encoded because it is not of string type', 'field' => $f, 'value' => $value]);
                }
                return base64_encode($value);
        }
    }