Ajax error: Trying to access array offset on value of type null

Re-roll of #9 for 3.x.

The patch from #11 works well here! Thank you!

I'm getting this error with PHP 8.1, D 9.5, and field_states_ui 3.0.0.

#11 seems to resolve it. Thank you!

Updating the title as this isn't just PHP 7.4.
Taking the leap here and moving to RTBC, it is being reported as valid, patch is small and looks good to me. Thank you @godotislate.

RTBC + 1 -> Working on Drupal 10.3.1