Lot of php warnings for this plug

The plugin creates a lot of PHP warnings.

[Wed Jan 18 08:23:34.067950 2023] Backend log: PHP Warning: Trying to access array offset on value of type bool in /home/testt/domains/testdomein.nl/public_html/wp-content/plugins/service-area-postcode-checker/options.php on line 20\n, referer: https://testdomein.nl/wp-admin/index.php
[Wed Jan 18 08:23:34.068122 2023] [host testdomein.nl] Backend log: PHP Warning: Undefined array key “title-display” in /home/testt/domains/testdomein.nl/public_html/wp-content/plugins/service-area-postcode-checker/options.php on line 328\n, referer: https://testdomein.nl/wp-admin/index.php
[Wed Jan 18 08:23:34.068152 2023] [host testdomein.nl] Backend log: PHP Warning: Undefined array key “class-display” in /home/testt/domains/testdomein.nl/public_html/wp-content/plugins/service-area-postcode-checker/options.php on line 344\n, referer: https://testdomein.nl/wp-admin/index.php
[Wed Jan 18 08:23:34.068185 2023] [host testdomein.nl] Backend log: PHP Warning: Undefined array key “class-bullet” in /home/testt/domains/testdomein.nl/public_html/wp-content/plugins/service-area-postcode-checker/options.php on line 360\n, referer: https://testdomein.nl/wp-admin/index.php
[Wed Jan 18 08:27:27.240071 2023] [host testdomein.nl] Backend log: PHP Warning: Trying to access array offset on value of type bool in /home/testt/domains/testdomein.nl/public_html/wp-content/plugins/service-area-postcode-checker/options.php on line 20\n, referer: https://testdomein.nl/wp-admin/plugins.php
[Wed Jan 18 08:27:27.240269 2023] [host testdomein.nl] Backend log: PHP Warning: Undefined array key “title-display” in /home/testt/domains/testdomein.nl/public_html/wp-content/plugins/service-area-postcode-checker/options.php on line 328\n, referer: https://testdomein.nl/wp-admin/plugins.php
[Wed Jan 18 08:27:27.240311 2023] [host testdomein.nl] Backend log: PHP Warning: Undefined array key “class-display” in /home/testt/domains/testdomein.nl/public_html/wp-content/plugins/service-area-postcode-checker/options.php on line 344\n, referer: https://testdomein.nl/wp-admin/plugins.php
[Wed Jan 18 08:27:27.240351 2023] [host testdomein.nl] Backend log: PHP Warning: Undefined array key “class-bullet” in /home/testt/domains/testdomein.nl/public_html/wp-content/plugins/service-area-postcode-checker/options.php on line 360\n, referer: https://testdomein.nl/wp-admin/plugins.php