Wordfence found error: Undefined index: badtlds

Wordfence scan reported the following errors:

Filename:	.../public_html/wp-content/plugins/stop-spammer-registrations-plugin/data/.sfs_debug_output.txt
File Size:	970 bytes
File last modified:	Saturday 18th of September 2021 08:42:33 PM

Time: 2021/09/13 13:45:25
Error Number: 8
Error Type: Run-time notices. Indicate that the script encountered something that could indicate an error, but could also happen in the normal course of running a script. 
Error Msg: Undefined index: badtlds
IP Address: 108.28.51.61
File Name: .../public_html/wp-content/plugins/stop-spammer-registrations-plugin/settings/settings.php
Line Number: 204
Memory Used: 14680064 Peak: 14680064
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Time: 2021/09/18 16:42:33
Error Number: 8
Error Type: Run-time notices. Indicate that the script encountered something that could indicate an error, but could also happen in the normal course of running a script. 
Error Msg: Undefined index: badtlds
IP Address: 108.28.51.61
File Name: .../public_html/wp-content/plugins/stop-spammer-registrations-plugin/settings/settings.php
Line Number: 204
Memory Used: 14680064 Peak: 14680064
---------------------