Fatal error: Uncaught TypeError: Argument 1 passed to Magento\Catalog\Model\ProductRepository::getProductFromLocalCache() must be of the type string, null given, called in /vendor/magento/module-catalog/Model/ProductRepository.php on line 270 and defined in vendor/magento/module-catalog/Model/ProductRepository.php:751
Possible reason is that there's a NULL sku in catalog_product_entity. To find out, query the catalog_product_entity table for a NULL sku. Something like: SELECT * FROM catalog_product_entity WHERE sku IS NULL; If there is, then just set the SKU and you're good!