{"code":"a8e82be8","stacktrace":"TypeError: Return value of Materials\\Model\\WorksheetModel::appendElements() must be of the type array, string returned in /var/app/current/module/Materials/src/Model/WorksheetModel.php:469\nStack trace:\n#0 /var/app/current/module/Materials/src/Model/WorksheetModel.php(52): Materials\\Model\\WorksheetModel->appendElements(Object(Application\\Model\\ArrayObject))\n#1 /var/app/current/module/Materials/src/Model/MaterialModel.php(339): Materials\\Model\\WorksheetModel->appendWorksheetData(Object(Application\\Model\\ArrayObject))\n#2 /var/app/current/module/Materials/src/Controller/MaterialTrait.php(74): Materials\\Model\\MaterialModel->getMaterial('m4bfrjwu', Object(Application\\Utils\\Parameters), Array)\n#3 /var/app/current/module/Materials/src/Controller/MaterialController.php(143): Materials\\Controller\\MaterialController->fetchMaterial('m4bfrjwu', Object(Application\\Utils\\Parameters), Array)\n#4 /var/app/current/vendor/laminas/laminas-mvc/src/Controller/AbstractRestfulController.php(373): Materials\\Controller\\MaterialController->get('m4bfrjwu')\n#5 /var/app/current/module/Application/src/Controller/GeoGebraController.php(93): Laminas\\Mvc\\Controller\\AbstractRestfulController->onDispatch(Object(Laminas\\Mvc\\MvcEvent))\n#6 /var/app/current/vendor/laminas/laminas-eventmanager/src/EventManager.php(319): Application\\Controller\\GeoGebraController->onDispatch(Object(Laminas\\Mvc\\MvcEvent))\n#7 /var/app/current/vendor/laminas/laminas-eventmanager/src/EventManager.php(179): Laminas\\EventManager\\EventManager->triggerListeners(Object(Laminas\\Mvc\\MvcEvent), Object(Closure))\n#8 /var/app/current/vendor/laminas/laminas-mvc/src/Controller/AbstractController.php(97): Laminas\\EventManager\\EventManager->triggerEventUntil(Object(Closure), Object(Laminas\\Mvc\\MvcEvent))\n#9 /var/app/current/vendor/laminas/laminas-mvc/src/Controller/AbstractRestfulController.php(307): Laminas\\Mvc\\Controller\\AbstractController->dispatch(Object(Laminas\\Http\\PhpEnvironment\\Request), Object(Laminas\\Http\\PhpEnvironment\\Response))\n#10 /var/app/current/vendor/laminas/laminas-mvc/src/DispatchListener.php(132): Laminas\\Mvc\\Controller\\AbstractRestfulController->dispatch(Object(Laminas\\Http\\PhpEnvironment\\Request), Object(Laminas\\Http\\PhpEnvironment\\Response))\n#11 /var/app/current/vendor/laminas/laminas-eventmanager/src/EventManager.php(319): Laminas\\Mvc\\DispatchListener->onDispatch(Object(Laminas\\Mvc\\MvcEvent))\n#12 /var/app/current/vendor/laminas/laminas-eventmanager/src/EventManager.php(179): Laminas\\EventManager\\EventManager->triggerListeners(Object(Laminas\\Mvc\\MvcEvent), Object(Closure))\n#13 /var/app/current/vendor/laminas/laminas-mvc/src/Application.php(325): Laminas\\EventManager\\EventManager->triggerEventUntil(Object(Closure), Object(Laminas\\Mvc\\MvcEvent))\n#14 /var/app/current/public/index.php(43): Laminas\\Mvc\\Application->run()\n#15 {main}"}