Slim Application Error

The application could not run because of the following error:

Details

Type: TypeError
Code: 0
Message: htmlspecialchars(): Argument #1 ($string) must be of type string, null given
File: /homepages/35/d144117733/htdocs/echecsforbach/src/controller/ClubController.php
Line: 66

Trace

#0 /homepages/35/d144117733/htdocs/echecsforbach/src/controller/ClubController.php(66): htmlspecialchars()
#1 /homepages/35/d144117733/htdocs/echecsforbach/vendor/slim/slim/Slim/Handlers/Strategies/RequestResponse.php(38): App\controller\ClubController->tournament()
#2 /homepages/35/d144117733/htdocs/echecsforbach/vendor/slim/slim/Slim/Routing/Route.php(358): Slim\Handlers\Strategies\RequestResponse->__invoke()
#3 /homepages/35/d144117733/htdocs/echecsforbach/vendor/slim/slim/Slim/MiddlewareDispatcher.php(65): Slim\Routing\Route->handle()
#4 /homepages/35/d144117733/htdocs/echecsforbach/vendor/slim/slim/Slim/MiddlewareDispatcher.php(65): Slim\MiddlewareDispatcher->handle()
#5 /homepages/35/d144117733/htdocs/echecsforbach/vendor/slim/slim/Slim/Routing/Route.php(315): Slim\MiddlewareDispatcher->handle()
#6 /homepages/35/d144117733/htdocs/echecsforbach/vendor/slim/slim/Slim/Routing/RouteRunner.php(68): Slim\Routing\Route->run()
#7 /homepages/35/d144117733/htdocs/echecsforbach/vendor/slim/slim/Slim/Middleware/ErrorMiddleware.php(76): Slim\Routing\RouteRunner->handle()
#8 /homepages/35/d144117733/htdocs/echecsforbach/vendor/slim/slim/Slim/MiddlewareDispatcher.php(121): Slim\Middleware\ErrorMiddleware->process()
#9 /homepages/35/d144117733/htdocs/echecsforbach/vendor/slim/slim/Slim/MiddlewareDispatcher.php(65): Psr\Http\Server\RequestHandlerInterface@anonymous->handle()
#10 /homepages/35/d144117733/htdocs/echecsforbach/vendor/slim/slim/Slim/App.php(199): Slim\MiddlewareDispatcher->handle()
#11 /homepages/35/d144117733/htdocs/echecsforbach/vendor/slim/slim/Slim/App.php(183): Slim\App->handle()
#12 /homepages/35/d144117733/htdocs/echecsforbach/public/index.php(486): Slim\App->run()
#13 {main}
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