Admin | Customers edit customer undefined key when customer fax turned off

[OldNGrey]

zc157d vanilla with PHP 8.0

Minor bug
Warning Undefined array key "customers_fax" in admin\customers.php on line 92.

This occurs when Admin | Configuration | Customer Details | Fax Number = false
and Customer Details are edited.

I changed (changes in red)

$customers_fax = zen_db_prepare_input($_POST['customers_fax'] );

to

$customers_fax = zen_db_prepare_input(($_POST['customers_fax'] ?? ''));