DB error

Fatal error: Uncaught Error: Undefined class constant 'ASYNC_KEY' in /home/clients1valivalc/src/EventsHandler.php:28 Stack trace: #0 /home/clients1valivalc/src/Controllers/Traits/ProductControllerTrait.php(432): Valival\EventsHandler::raiseEvent(7, Array) #1 [internal function]: Valival\ProductController::index(Array) #2 /home/clients1valivalc/public/index.php(76): call_user_func_array('Valival\\Product...', Array) #3 {main} thrown in /home/clients1valivalc/src/EventsHandler.php on line 28