500 Internal Server Error

Trying to access array offset on value of type null (2)

#0 /home/ipanelon/technologycore.fun/app/inc/join.php(8): flight\Engine->handleError()
#1 /home/ipanelon/technologycore.fun/index.php(38): include('/home/ipanelon/...')
#2 [internal function]: {closure}()
#3 /home/ipanelon/vendor/flightphp/core/flight/core/Dispatcher.php(354): call_user_func_array()
#4 /home/ipanelon/vendor/flightphp/core/flight/core/Dispatcher.php(287): flight\core\Dispatcher->invokeCallable()
#5 /home/ipanelon/vendor/flightphp/core/flight/Engine.php(548): flight\core\Dispatcher->execute()
#6 [internal function]: flight\Engine->_start()
#7 /home/ipanelon/vendor/flightphp/core/flight/core/Dispatcher.php(376): call_user_func_array()
#8 /home/ipanelon/vendor/flightphp/core/flight/core/Dispatcher.php(287): flight\core\Dispatcher->invokeCallable()
#9 /home/ipanelon/vendor/flightphp/core/flight/core/Dispatcher.php(131): flight\core\Dispatcher->execute()
#10 /home/ipanelon/vendor/flightphp/core/flight/core/Dispatcher.php(95): flight\core\Dispatcher->runEvent()
#11 /home/ipanelon/vendor/flightphp/core/flight/Engine.php(118): flight\core\Dispatcher->run()
#12 /home/ipanelon/vendor/flightphp/core/flight/Flight.php(124): flight\Engine->__call()
#13 /home/ipanelon/technologycore.fun/index.php(93): Flight::__callStatic()
#14 {main}