Joomla allows to use different primary key names for tables. This has not been honoured in the JsonApiView::displayItem() function.

Steps to reproduce the issue

Create a new API accessing data from a component which has a table with a primary key which is not called 'id'.
The view class for the API extends Joomla\CMS\MVC\View\JsonApiView.
Execute the API GET for a specific item id which exists in the table.

Expected result

The item should be returned by the webservice.

Actual result

Warning: Undefined property: Joomla\CMS\Object\CMSObject::$id in
/home/customer/www/dev4.spindata.co.uk/public_html/libraries/src/MVC/View/JsonApiView.php on line 218

This is because line 218 of the displayItem()function in Joomla\CMS\MVC\View\JsonApiView checks if $item->id is null, but $item->id does not exist:

if ($item->id === null) {
throw new RouteNotFoundException('Item does not exist');
}

System information (as much as possible)

Joomla version 4.2.5

Additional comments