Coming across some deprecated errors with 8.1 I want to address.
PHP Deprecated: explode(): Passing null to parameter #2 ($string) of type string is deprecated in...
//explode uids into an array
$comp_uids = explode(',', $result['comp_uids']);
$result['comp_uids'] in this case is empty which is why the null error shows. I'm not sure why they are deprecating this ability, but what is the recommended change to avoid this? I'm seeing similar with strlen(): Passing null to parameter #1 ($string) of type string is deprecated and a few others using 8.1.
Use the null coalescing operator to default the value to an empty string if the value is null.
$comp_uids = explode(',', $result['comp_uids'] ?? '');
There's no need to explode null, you know beforehand that it won't return matches. If you really want [''] as result, it's more intuitive to do it explicit:
$comp_uids = $result['comp_uids'] !== null ? explode(',', $result['comp_uids']) : [''];
I still find this a bit counter-intuitive for your fellow programmers. IMHO, the no UIDs were found concept is better represented by an empty array and, if you can expect empty strings as well, they may well be handled together with null:
$comp_uids = $result['comp_uids'] != '' ? explode(',', $result['comp_uids']) : [];
Just cast the parameter as string, will convert null to ''.
$comp_uids = explode(',', (string)$result['comp_uids']);