Magento2 developer -- 3

I'm now installing and learning Magento2.3.1. I have got error following HTTP error 500. [php7:error] [pid 5570] [client [login to view URL]] PHP Fatal error: Uncaught Error: Call to a member function getData() on null in /var/www/html/app/design/frontend/Smartwave/porto/Magento_Catalog/templates/product/view/[login to view URL]\nStack trace:\n#0 /var/www/html/vendor/magento/framework/View/TemplateEngine/[login to view URL](59): include()\n#1 /var/www/html/vendor/magento/framework/View/Element/[login to view URL](271): Magento\\Framework\\View\\TemplateEngine\\Php->render(Object(Magento\\Catalog\\Block\\Product\\View\\Details), '/var/www/html/a...', Array)\n#2 /var/www/html/vendor/magento/framework/View/Element/[login to view URL](301): Magento\\Framework\\View\\Element\\Template->fetchView('/var/www/html/a...')\n#3 /var/www/html/vendor/magento/framework/View/Element/[login to view URL](668): Magento\\Framework\\View\\Element\\Template->_toHtml()\n#4 /var/www/html/vendor/magento/framework/View/[login to view URL](557): Magento\\Framework\\View\\Element\\AbstractBlock->toHtml()\n#5 /var/www/html/vendor/magento/framework/View/[login to view URL](533): Magento\\Framework\\View\\Layout->_renderBlock('product.info.de...')\n#6 /var/www/html/generated in /var/www/html/app/design/frontend/Smartwave/porto/Magento_Catalog/templates/product/view/[login to view URL] on line 18, referer: Please advice me for solve this problem. I am looking for someone who can give me advice on an ongoing basis.