Fatal error: Uncaught TypeError: Argument 1 passed to Magento\Catalog\Model\ProductRepository::prepareSku() must be of the type string, null given, called in /var/www/html/vendor/magento/module-catalog/Model/ProductRepository.php on line 790 and defined in /var/www/html/vendor/magento/module-catalog/Model/ProductRepository.php:800
Stack trace:
#0 /var/www/html/vendor/magento/module-catalog/Model/ProductRepository.php(790): Magento\Catalog\Model\ProductRepository->prepareSku(NULL)
#1 /var/www/html/vendor/magento/module-catalog/Model/ProductRepository.php(349): Magento\Catalog\Model\ProductRepository->saveProductInLocalCache(Object(Magento\Catalog\Model\Product\Interceptor), 'adf0bb68589672e...')
#2 /var/www/html/vendor/magento/module-catalog/Model/ProductRepository.php(314): Magento\Catalog\Model\ProductRepository->cacheProduct('adf0bb68589672e...', Object(Magento\Catalog\Model\Product\Interceptor))
#3 /var/www/html/app/code/Amasty/Groupcat/Observer/Product/ViewPredispatch.php(79): Magento\Catalog\Model\ProductRepository-> in /var/www/html/vendor/magento/module-catalog/Model/ProductRepository.php on line 800