We are importing data from an ERP system using this example code

public function createProductRecords($productDataArray, $productId)
{

    $productRecord['id'] = $productId;
    if (isset($productDataArray['productNumber'])) {
        $productRecord['productNumber'] = $productDataArray['productNumber'];

    }

    if (isset($productDataArray['stock'])) {
        $productRecord['stock'] = intval($productDataArray['stock']);

But we need to add custom data in this import method, I have tried the following approach:

if (isset($productDataArray['customFields.custom_outer'])) 
{
            $productRecord['customFields.custom_outer'] = $productDataArray['customFields.custom_outer'];

}
return $productRecord;