PHP Notice

Hello,
First at all, thank you very much for this real great plugin.

Since last update (WP 5.9 | Perfecty Push Notifications – 1.5.1),
Perfecty Push shows me a Notice when i’m posting a form in backoffice (create or update a post for example)

PHP Notice:  Undefined index: perfecty_push_notification_custom_title in .../wp-content/plugins/perfecty-push-notifications/admin/class-perfecty-push-admin.php on line 590
[02-Feb-2022 16:20:13 UTC] PHP Notice:  Undefined index: perfecty_push_notification_custom_body in .../wp-content/plugins/perfecty-push-notifications/admin/class-perfecty-push-admin.php on line 591
[02-Feb-2022 16:20:13 UTC] PHP Notice:  Undefined index: perfecty_push_notification_custom_title in .../wp-content/plugins/perfecty-push-notifications/admin/class-perfecty-push-admin.php on line 564
[02-Feb-2022 16:20:13 UTC] PHP Notice:  Undefined index: perfecty_push_notification_custom_body in .../wp-content/plugins/perfecty-push-notifications/admin/class-perfecty-push-admin.php on line 567

since i need to display error for a perfect development, it break hte page because of
Cannot modify header information - headers already sent by (output started at .../wp-content/plugins/perfecty-push-notifications/admin/class-perfecty-push-admin.php:590)

Could you please help me with this.

thank you