Slim Application Error

The application could not run because of the following error:
Details

Type: Error
Code: 0
Message: Value of type null is not callable
File: /www/htdocs/w01744b9/koemmerling-frontale.com/routes/api.php
Line: 1468
Trace

#0 /www/htdocs/w01744b9/koemmerling-frontale.com/vendor/slim/slim/Slim/Handlers/Strategies/RequestResponse.php(38): Closure->{closure:/www/htdocs/w01744b9/koemmerling-frontale.com/routes/api.php:1466}(Object(Slim\Psr7\Request), Object(Slim\Psr7\Response), Array)
#1 /www/htdocs/w01744b9/koemmerling-frontale.com/vendor/slim/slim/Slim/Routing/Route.php(358): Slim\Handlers\Strategies\RequestResponse->__invoke(Object(Closure), Object(Slim\Psr7\Request), Object(Slim\Psr7\Response), Array)
#2 /www/htdocs/w01744b9/koemmerling-frontale.com/vendor/slim/slim/Slim/MiddlewareDispatcher.php(65): Slim\Routing\Route->handle(Object(Slim\Psr7\Request))
#3 /www/htdocs/w01744b9/koemmerling-frontale.com/vendor/slim/slim/Slim/MiddlewareDispatcher.php(65): Slim\MiddlewareDispatcher->handle(Object(Slim\Psr7\Request))
#4 /www/htdocs/w01744b9/koemmerling-frontale.com/vendor/slim/slim/Slim/Routing/Route.php(315): Slim\MiddlewareDispatcher->handle(Object(Slim\Psr7\Request))
#5 /www/htdocs/w01744b9/koemmerling-frontale.com/vendor/slim/slim/Slim/Routing/RouteRunner.php(68): Slim\Routing\Route->run(Object(Slim\Psr7\Request))
#6 /www/htdocs/w01744b9/koemmerling-frontale.com/vendor/bryanjhv/slim-session/src/Slim/Middleware/Session.php(82): Slim\Routing\RouteRunner->handle(Object(Slim\Psr7\Request))
#7 /www/htdocs/w01744b9/koemmerling-frontale.com/vendor/slim/slim/Slim/MiddlewareDispatcher.php(269): Slim\Middleware\Session->__invoke(Object(Slim\Psr7\Request), Object(Slim\Routing\RouteRunner))
#8 /www/htdocs/w01744b9/koemmerling-frontale.com/vendor/slim/slim/Slim/Middleware/RoutingMiddleware.php(45): Psr\Http\Server\RequestHandlerInterface@anonymous->handle(Object(Slim\Psr7\Request))
#9 /www/htdocs/w01744b9/koemmerling-frontale.com/vendor/slim/slim/Slim/MiddlewareDispatcher.php(121): Slim\Middleware\RoutingMiddleware->process(Object(Slim\Psr7\Request), Object(Psr\Http\Server\RequestHandlerInterface@anonymous))
#10 /www/htdocs/w01744b9/koemmerling-frontale.com/vendor/slim/slim/Slim/Middleware/BodyParsingMiddleware.php(64): Psr\Http\Server\RequestHandlerInterface@anonymous->handle(Object(Slim\Psr7\Request))
#11 /www/htdocs/w01744b9/koemmerling-frontale.com/vendor/slim/slim/Slim/MiddlewareDispatcher.php(121): Slim\Middleware\BodyParsingMiddleware->process(Object(Slim\Psr7\Request), Object(Psr\Http\Server\RequestHandlerInterface@anonymous))
#12 /www/htdocs/w01744b9/koemmerling-frontale.com/vendor/slim/slim/Slim/Middleware/ErrorMiddleware.php(76): Psr\Http\Server\RequestHandlerInterface@anonymous->handle(Object(Slim\Psr7\Request))
#13 /www/htdocs/w01744b9/koemmerling-frontale.com/vendor/slim/slim/Slim/MiddlewareDispatcher.php(121): Slim\Middleware\ErrorMiddleware->process(Object(Slim\Psr7\Request), Object(Psr\Http\Server\RequestHandlerInterface@anonymous))
#14 /www/htdocs/w01744b9/koemmerling-frontale.com/vendor/slim/slim/Slim/MiddlewareDispatcher.php(65): Psr\Http\Server\RequestHandlerInterface@anonymous->handle(Object(Slim\Psr7\Request))
#15 /www/htdocs/w01744b9/koemmerling-frontale.com/vendor/slim/slim/Slim/App.php(199): Slim\MiddlewareDispatcher->handle(Object(Slim\Psr7\Request))
#16 /www/htdocs/w01744b9/koemmerling-frontale.com/vendor/slim/slim/Slim/App.php(183): Slim\App->handle(Object(Slim\Psr7\Request))
#17 /www/htdocs/w01744b9/koemmerling-frontale.com/public/index.php(52): Slim\App->run()
#18 {main}