PHP Notice: Undefined index

Hi,

Plugin version: Version 2.1

With debug.log enabled, I am seeing the below notice when updating tracking number ans setting the status to Shipped.

[02-Jul-2019 07:41:51 UTC] PHP Notice:  Undefined index: custom_tracking_provider in path/wp-content/plugins/woo-advanced-shipment-tracking/includes/class-wc-advanced-shipment-tracking.php on line 589
[02-Jul-2019 07:41:51 UTC] PHP Notice:  Undefined index: custom_tracking_link in path/wp-content/plugins/woo-advanced-shipment-tracking/includes/class-wc-advanced-shipment-tracking.php on line 590
[02-Jul-2019 07:41:51 UTC] PHP Notice:  Undefined index: status_shipped in path/wp-content/plugins/woo-advanced-shipment-tracking/includes/class-wc-advanced-shipment-tracking.php on line 593

Please review and advise / fix.

Thanks