500 error during creating shipment for order with configurable product on custom stock

[smoskaluk]

Preconditions

1. Magento MSI
2. Custom stock with custom source created and assigned to Main website
3. Configurable product created with child product assigned to custom source

Steps to reproduce

1. Make order with created configurable product with qty = 1
2. Open new order in admin and try to create shipment for it

Expected result

1. Shipment created successfully

Actual result

1. HTTP ERROR 500
   PHP Fatal error: Uncaught RuntimeException: Can't create directory /var/www/html/magento2ce/var/generation/Magento/Framework/App/ResourceConnection/Config/. in /var/www/html/magento2ce/l
   ib/internal/Magento/Framework/Code/Generator.php:115\nStack trace:\n#0 /var/www/html/magento2ce/lib/internal/Magento/Framework/Code/Generator/Autoloader.php(35): Magento\Framework\Code\Generator->generateClass('Magento\\Framewo...')\n#1 [internal function]: Magento
   \Framework\Code\Generator\Autoloader->load('Magento\\Framewo...')\n#2 [internal function]: spl_autoload_call('Magento\\Framewo...')\n#3 /var/www/html/magento2ce/lib/internal/Magento/Framework/ObjectManager/Relations/Runtime.php(38): class_exists('Magento\\Framework