private function customFieldInstance($prefix): array
    {
        $ns = $this->xmlns[$prefix];

        if (!$discoveredCustomField = $this->customFields[$ns]) {
            throw new LogicException(
                sprintf(
                    'No custom field class was found for %s. setCustomFields() must be called before using this extractor.',
                    $ns
                )
            );
        }

        return [new Type('object', false, $discoveredCustomField->getClass())];
    }