Emailing backups doesn’t work in WordPress > 5.0

Hi,

Since August 24th, I updated WordPress (I cannot remember exactly when), I can see errors in Logs for the CRON Tasks at my hosting provider.

Undefined index: SERVER_NAME

Then, following some help from some forums, I update my “wp-config.php” file with
if (!isset($_SERVER['SERVER_NAME'])) $_SERVER['SERVER_NAME']="localhost";

Now, in the CRON Logs, I can see error :
Undefined variable: headers

There is something wrong with the forms field and variable that seem to not be defined by WP-DB-BACKUP since WordPress 5.0 or above

It’s confirmed. If I disable WP_DB_BACKUP plugin, my CRON Job runs without any error.

For me, regarding the error Undefined variable: headers
The error is certainly somewhere below (line 1002) :

	$headers .= "MIME-Version: 1.0\n";
	$headers = 'From: wordpress@' . preg_replace('#^www\.#', '', sanitize_text_field(strtolower($_SERVER['SERVER_NAME']))) . "\n";
	$headers .= "Content-Type: multipart/mixed; boundary=\"$boundary\"\n";