Fatal error: Uncaught PDOException: SQLSTATE[23000]: Integrity constraint violation: 1062 Duplicate entry 'NULL' for key 'sessions.sessions_user_id' in /var/www/clients/client1/web1/web/lib/pkp/lib/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php:115 Stack trace: #0 /var/www/clients/client1/web1/web/lib/pkp/lib/vendor/doctrine/dbal/lib/Doctrine/DBAL/Driver/PDOStatement.php(115): PDOStatement->execute() #1 /var/www/clients/client1/web1/web/lib/pkp/lib/vendor/laravel/framework/src/Illuminate/Database/Connection.php(489): Doctrine\DBAL\Driver\PDOStatement->execute() #2 /var/www/clients/client1/web1/web/lib/pkp/lib/vendor/laravel/framework/src/Illuminate/Database/Connection.php(664): Illuminate\Database\Connection->Illuminate\Database\{closure}() #3 /var/www/clients/client1/web1/web/lib/pkp/lib/vendor/laravel/framework/src/Illuminate/Database/Connection.php(631): Illuminate\Database\Connection->runQueryCallback() #4 /var/www/clients/client1/web1/web/lib/pkp/lib/vendor/laravel/framework/src/Illuminate/Database/Co in /var/www/clients/client1/web1/web/lib/pkp/lib/vendor/laravel/framework/src/Illuminate/Database/Connection.php on line 671