Struggling at getting Flarum installed and continually hitting issues with Zend Stratigility (error below). I started with a vanilla install, no migration and fresh Ubuntu 18.04 LTS with PHP 7.1. All the neccessary PHP extensions (dom, gd, json, mbstring, openssl, pdo_mysql, tokenizer) are installed.
Fatal error: Uncaught TypeError: Return value of Zend\Stratigility\MiddlewarePipe::pipe() must be an instance of Zend\Stratigility\void, none returned in /var/www/data/flarum/vendor/zendframework/zend-stratigility/src/MiddlewarePipe.php:100 Stack trace: #0 /var/www/data/flarum/vendor/flarum/core/src/Install/Installer.php(40): Zend\Stratigility\MiddlewarePipe->pipe(Object(Flarum\Http\Middleware\HandleErrorsWithWhoops)) #1 /var/www/data/flarum/vendor/flarum/core/src/Http/Server.php(37): Flarum\Install\Installer->getRequestHandler() #2 /var/www/public_html/iris/index.php(22): Flarum\Http\Server->listen() #3 {main} thrown in /var/www/data/flarum/vendor/zendframework/zend-stratigility/src/MiddlewarePipe.php on line 100
To be honest, not really sure where to look now to attempt to fix this - all files (apart from index.php which has been updated to show the correct directory) are as per those that would have been created during installation via Composer. No errors appeared during installation.
If anyone can share any ideas on what could be the cause, it would be appreciated,