TypeError: stripos(): Argument #1 ($haystack) must be of type string, null given

in /home/u862342697/domains/elcbd.es/cbdlleida-app/app/controllers/ProductController.php:168

#0 /home/u862342697/domains/elcbd.es/cbdlleida-app/app/controllers/ProductController.php(168): stripos()
#1 /home/u862342697/domains/elcbd.es/cbdlleida-app/app/lib/Router.php(102): App\Controllers\ProductController->show()
#2 /home/u862342697/domains/elcbd.es/cbdlleida-app/app/lib/Router.php(88): App\Lib\Router->invoke()
#3 /home/u862342697/domains/elcbd.es/cbdlleida-app/public/index.php(90): App\Lib\Router->dispatch()
#4 /home/u862342697/domains/elcbd.es/public_html/index.php(1): require('/home/u86234269...')
#5 {main}