TypeError in laravel-backup 9.2.0 when mail.to config is null

[andreasnij]

After upgrading from laravel-backup 8 to laravel-backup 9.2.0 I get this error when running any test in my test suite:

TypeError: Spatie\Backup\Exceptions\InvalidConfig::invalidEmail(): Argument #1 ($email) must be of type string, null given

This is in part because I use an environment variable for the mail.to config in the backup.php config file which is not set in my test environment:

'mail' => [
    'to' => env('ERROR_MAIL_ADDRESS'),

I think the email config should be allowed to be null like in version 8, for people who don't want email notifications or test environments.

Another concern I have is that the laravel-backup config is parsed even though never used (I don't have any tests for laravel-backup in my test suite). I think this has something to do with Spatie\Backup\Config\Config being injected in the laravel backup commands' constructors.