TypeError: in_array(): Argument #2 ($haystack) must be of type array, null given in in_array()

Hmm this doesn't seem to be a correct solution for the problem. You bail out on the function and do not allow the following code to be executed.
There is indeed a need for a check. And when the class array does not exist, add it.

Ah now i see, the solution is correct here as the code does not have any more need to be executed.
I'm not using the modal, so didn't got into this situation.

Can you elaborate on what versions you are using so one can try to reproduce this?

@tim, After saving the block, i am getting this warning only. https://prnt.sc/v0CUXYyKihjx
Not sure if it is relevant to error @stefan got. I am using Drupal 10.2 and my PHP version is 8.1

Automatically closed - issue fixed for 2 weeks with no activity.