Trying to access array offset on value of type null error

Using ConcreteCMS 9.1.2
PHP 8.1.11
It goes away if I switch back to PHP 7.3, it happens when I Update a product in community store. I have posted it on the Community Store GitHub page as well.

Error “/updates/concrete-cms-9.1.2/concrete/attributes/select/controller.php”

        if ($akSelectAllowMultipleValues && !$akSelectAllowOtherValues) {
            // checkbox list.  No new options.
            $options = [];
            if (is_array($data['atSelectOptionValue'])) {             <- Error on this line (260)
                foreach ($data['atSelectOptionValue'] as $optionID) {
                    $option = $this->getOptionByID($optionID);
                    if (is_object($option)) {
                        $options[] = $option;

It looks like this is a bug.

If you use an attribute Option List and use the Select Option Allow multiple options… and you do not choose an option on your community store product page for that attribute, it throws the above error.

Upgraded to 9.1.3 and that did not fix it.

Hi @mdius - is this this the Github issue?

Was this bit what ended up working for you?

Had this error on my clean install test site and I manually turned on Database Entities - Doctrine Development Mode and then re-run script, and that worked for that site.

No, for this issue I had to edit the core system, but Mesuva submitted it as a bug, so maybe it’ll be fixed in the next release.

But I did this:
Edit the file /updates/concrete-cms-9.1.2/concrete/attributes/select/controller.php
Line 260
if (is_array($data['atSelectOptionValue'])) {
Change it to
if (isset($data['atSelectOptionValue']) && is_array($data['atSelectOptionValue'])) {