GitLab

It's probably not limited to new individual, but this recent commit added a line that generates the notice:

$fieldAttributes['class'] .= ltrim($fieldAttributes['class'] ?? '' . ' crm-select2');

You can't use .= if the variable isn't set yet, so this gives a red error box on the form. I thought I had written a test to catch generic red boxes on New Individual but maybe it's not a complete test.

Also while it ends up not mattering here, on the right-hand-side personally I think it's best to use brackets to be clear when using ?? and . at the same time, since the . ends up winning and can sometimes be a sneaky bug.