TypeError: Unsupported operand types: array + null

We finally got to the bottom of this and it was a weird situation.

We are filling a select2 field on the fly with

$nodeStorage = $this->entityTypeManager->getStorage('node');
$nodeQuery = $nodeStorage->getQuery();

Then it's supposed to filter based on node type...

$custom_node_type_ids = $nodeQuery
        ->condition('type', 'custom_node_type')
        ->condition('status', 1)
        ->sort('created', 'DESC')
        ->accessCheck()
        ->execute();

But for some reason, when I debug the output from this function, it returns not only the custom_node_type nodes, but also the node of the current page. The current page is of the "page" content type, but that doesn't seem to matter to the nodeQuery.

I had to add the following:

$my_nodes_ids = $nodeQuery
        ->condition('type', 'my_nodes')
        ->condition('status', 1)
        ->sort('created', 'DESC')
        ->condition('nid', '4856', '!=')
        ->accessCheck()
        ->execute();

After that, my function that was filling the select2 field no longer had null values for the fields it was trying to reference.

I suspect this has always been a problem and Drupal just passed over the null value before, but now it's less forgiving of sloppy code.

At any rate, this is not a priblem with select2 at all.