What's the exact error message? It might have a little more information on what is happening exactly (or where it is happening).

The "uninitialized value" warning is actually disabled by default, and enabled either with use warnings, or the -w / -W / -X options, or the $^W variable. So maybe there's some config somewhere or another module that changes warnings activation. You can try this in your test version to see if the warnings appear:

{
  use warnings 'uninitialized';
  $update_or_insert->bind_param(10, $thing_id, SQL_INTEGER);
  $update_or_insert->bind_param(11, $action, SQL_VARCHAR );
}
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If the warning appears, your code had the issue all along, but just didn't tell you about it. In that case, perl just silently replaces your value by either "" or 0 depending on context, so you can do it explicitly to obtain the same result.

You could also try no warnings 'uninitialized'; in your shadow test version, but it's better to fix the warnings than just hide.

Edit: it looks like -X will disable all warnings regardless of whatever else you try to do, so the use warnings; wouldn't have any effect in that case.