Error Finish Lesson

{
        "message": "Trying to access array offset on value of type null",
        "exception": "ErrorException",
        "file": "/var/www/html/eie-rebase/app/Http/Controllers/LessonController.php",
        "line": 563,
        "trace": [
            {
                "file": "/var/www/html/eie-rebase/app/Http/Controllers/LessonController.php",
                "line": 563,
                "function": "handleError",
                "class": "Illuminate\\Foundation\\Bootstrap\\HandleExceptions",
                "type": "->"
            },
            {
                "file": "/var/www/html/eie-rebase/vendor/laravel/framework/src/Illuminate/Routing/Controller.php",
                "line": 54,
                "function": "finishLesson",
                "class": "App\\Http\\Controllers\\LessonController",
                "type": "->"
            },
            {
                "file": "/var/www/html/eie-rebase/vendor/laravel/framework/src/Illuminate/Routing/ControllerDispatcher.php",
                "line": 45,
                "function": "callAction",
                "class": "Illuminate\\Routing\\Controller",
                "type": "->"
            },
            {
                "file": "/var/www/html/eie-rebase/vendor/laravel/framework/src/Illuminate/Routing/Route.php",
                "line": 262,
                "function": "dispatch",
                "class": "Illuminate\\Routing\\ControllerDispatcher",
                "type": "->"
            },
            {
                "file": "/var/www/html/eie-rebase/vendor/laravel/framework/src/Illuminate/Routing/Route.php",
                "line": 205,
                "function": "runController",
                "class": "Illuminate\\Routing\\Route",
                "type": "->"
            },
            {
                "file": "/var/www/html/eie-rebase/vendor/laravel/framework/src/Illuminate/Routing/Router.php",
                "line": 695,
                "function": "run",
                "class": "Illuminate\\Routing\\Route",
                "type": "->"
            },
            {
                "file": "/var/www/html/eie-rebase/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php",
                "line": 128,
                "function": "Illuminate\\Routing\\{closure}",
                "class": "Illuminate\\Routing\\Router",
                "type": "->"
            },
            {
                "file": "/var/www/html/eie-rebase/vendor/laravel/framework/src/Illuminate/Routing/Middleware/SubstituteBindings.php",
                "line": 50,
                "function": "Illuminate\\Pipeline\\{closure}",
                "class": "Illuminate\\Pipeline\\Pipeline",
                "type": "->"
            },
            {
                "file": "/var/www/html/eie-rebase/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php",
                "line": 167,
                "function": "handle",
                "class": "Illuminate\\Routing\\Middleware\\SubstituteBindings",
                "type": "->"
            },
            {
                "file": "/var/www/html/eie-rebase/vendor/laravel/framework/src/Illuminate/Routing/Middleware/ThrottleRequests.php",
                "line": 127,
                "function": "Illuminate\\Pipeline\\{closure}",
                "class": "Illuminate\\Pipeline\\Pipeline",
                "type": "->"
            },
            {
                "file": "/var/www/html/eie-rebase/vendor/laravel/framework/src/Illuminate/Routing/Middleware/ThrottleRequests.php",
                "line": 103,
                "function": "handleRequest",
                "class": "Illuminate\\Routing\\Middleware\\ThrottleRequests",
                "type": "->"
            },
            {
                "file": "/var/www/html/eie-rebase/vendor/laravel/framework/src/Illuminate/Routing/Middleware/ThrottleRequests.php",
                "line": 55,
                "function": "handleRequestUsingNamedLimiter",
                "class": "Illuminate\\Routing\\Middleware\\ThrottleRequests",
                "type": "->"
            },
            {
                "file": "/var/www/html/eie-rebase/vendor/laravel/framework/src/Illuminate/Pipeline/Pipeline.php",
                "line": 167,
                "function": "handle",
                "class": "Illuminate\\Routing\\Middleware\\ThrottleRequests",
                "type": "->"
            },
            {
                "file": "/var/www/htm