Fresh installed laravel 5.6 getting HTTP ERROR 500 in index page

Hi everyone I'm having a hard time debugging an issue in laravel 5.6 freshly installed after upgrading from php 7.0 to php 7.1. I've already generated an app key for my test project. Changed owner to www-data and permission to 777 since it's just a test project.

Restarting php 7.1 fpm and NGINX is also done.

Please note that I can be able to run the project after running php aritsan serve command.

laravel.log

[2018-02-27 02:45:28] local.ERROR: Parse error: syntax error, unexpected '?', expecting variable (T_VARIABLE) {"exception":"[object] (Symfony\\Component\\Debug\\Exception\\FatalThrowableError(code: 0): Parse error: syntax error, unexpected '?', expecting variable (T_VARIABLE) at /development/sites/www/laravelAuth/vendor/symfony/finder/Comparator/NumberComparator.php:42)
[stacktrace]
#0 /development/sites/www/laravelAuth/vendor/composer/ClassLoader.php(301): Composer\\Autoload\\includeFile('/development/si...')
#1 [internal function]: Composer\\Autoload\\ClassLoader->loadClass('Symfony\\\\Compone...')
#2 /development/sites/www/laravelAuth/vendor/symfony/finder/Finder.php(120): spl_autoload_call('Symfony\\\\Compone...')
#3 /development/sites/www/laravelAuth/vendor/laravel/framework/src/Illuminate/Filesystem/Filesystem.php(420): Symfony\\Component\\Finder\\Finder->depth(0)
#4 /development/sites/www/laravelAuth/vendor/laravel/framework/src/Illuminate/Foundation/Exceptions/Handler.php(381): Illuminate\\Filesystem\\Filesystem->directories('/development/si...')
#5 /development/sites/www/laravelAuth/vendor/laravel/framework/src/Illuminate/Support/helpers.php(1038): Illuminate\\Foundation\\Exceptions\\Handler->Illuminate\\Foundation\\Exceptions\\{closure}(Object(Whoops\\Handler\\PrettyPageHandler))
#6 /development/sites/www/laravelAuth/vendor/laravel/framework/src/Illuminate/Foundation/Exceptions/Handler.php(384): tap(Object(Whoops\\Handler\\PrettyPageHandler), Object(Closure))
#7 /development/sites/www/laravelAuth/vendor/laravel/framework/src/Illuminate/Foundation/Exceptions/Handler.php(334): Illuminate\\Foundation\\Exceptions\\Handler->whoopsHandler()
#8 /development/sites/www/laravelAuth/vendor/laravel/framework/src/Illuminate/Support/helpers.php(1038): Illuminate\\Foundation\\Exceptions\\Handler->Illuminate\\Foundation\\Exceptions\\{closure}(Object(Whoops\\Run))
#9 /development/sites/www/laravelAuth/vendor/laravel/framework/src/Illuminate/Foundation/Exceptions/Handler.php(339): tap(Object(Whoops\\Run), Object(Closure))
#10 /development/sites/www/laravelAuth/vendor/laravel/framework/src/Illuminate/Foundation/Exceptions/Handler.php(314): Illuminate\\Foundation\\Exceptions\\Handler->renderExceptionWithWhoops(Object(Symfony\\Component\\Debug\\Exception\\FatalThrowableError))
#11 /development/sites/www/laravelAuth/vendor/laravel/framework/src/Illuminate/Foundation/Exceptions/Handler.php(287): Illuminate\\Foundation\\Exceptions\\Handler->convertExceptionToResponse(Object(Symfony\\Component\\Debug\\Exception\\FatalThrowableError))
#12 /development/sites/www/laravelAuth/vendor/laravel/framework/src/Illuminate/Foundation/Exceptions/Handler.php(188): Illuminate\\Foundation\\Exceptions\\Handler->prepareResponse(Object(Illuminate\\Http\\Request), Object(Symfony\\Component\\Debug\\Exception\\FatalThrowableError))
#13 /development/sites/www/laravelAuth/app/Exceptions/Handler.php(51): Illuminate\\Foundation\\Exceptions\\Handler->render(Object(Illuminate\\Http\\Request), Object(Symfony\\Component\\Debug\\Exception\\FatalThrowableError))
#14 /development/sites/www/laravelAuth/vendor/laravel/framework/src/Illuminate/Foundation/Http/Kernel.php(326): App\\Exceptions\\Handler->render(Object(Illuminate\\Http\\Request), Object(Symfony\\Component\\Debug\\Exception\\FatalThrowableError))
#15 /development/sites/www/laravelAuth/vendor/laravel/framework/src/Illuminate/Foundation/Http/Kernel.php(124): Illuminate\\Foundation\\Http\\Kernel->renderException(Object(Illuminate\\Http\\Request), Object(Symfony\\Component\\Debug\\Exception\\FatalThrowableError))
#16 /development/sites/www/laravelAuth/public/index.php(55): Illuminate\\Foundation\\Http\\Kernel->handle(Object(Illuminate\\Http\\Request))
#17 {main}
"} 
[2018-02-27 02:45:28] local.ERROR: Exception thrown without a stack frame {"exception":"[object] (Symfony\\Component\\Debug\\Exception\\FatalErrorException(code: 16): Exception thrown without a stack frame at Unknown:0)
[stacktrace]
#0 {main}
"} 

NGINX Server Config

server {
    listen 80;

    root /development/sites/www/laravelAuth/public;
    index index.php index.html index.htm index.nginx-debian.html;
    server_name laraveltestauth.ng www.laraveltestauth.ng;

    location / {
        try_files $uri $uri/ /index.php?$query_string;
    }

    location ~ \.php$ {
        try_files $uri /index.php =404;
        fastcgi_split_path_info ^(.+\.php)(/.+)$;
        fastcgi_pass  127.0.0.1:9000;
        fastcgi_index index.php;
        fastcgi_param SCRIPT_FILENAME $document_root$fastcgi_script_name;
        include fastcgi_params;
    }

    location ~ /\.ht {
        deny all;
    }
}

Hosthack

127.0.1.1   laraveltestauth.ng          www.laraveltestauth.ng

Let me know if there's anything I can add. Thanks in advance

via Chebli Mohamed