Data NULL with hook processDatamap_afterDatabaseOperations()

Question

I'm a new user of typo3 and I'm using the "processDatamap_afterDatabaseOperations" to send a notification to users when I create alerts messages with my extension.

        $storagePid = $hookObjectsArr->getPID($table, $id);
        $pageTsConfig = BackendUtility::getPagesTSconfig($storagePid);
        $this->settings = $pageTsConfig['tx_alerte.'];
        if ($table === 'tx_Myappalerte_domain_model_alerte' && ($this->settings['enabled'] === '1')) {
<mycode>
}

My issue is when I create a new alert, I have an error message because all my variables ($storagePid, $pageTsConfig, $this->settings) are NULL, I checked it with var_dump, but when I'm updating an existing alert, theses variables aren't NULL. I know the ID is obviously NULL because the alert isn't created

Is there a way to make what I want to do work?

thanks you