Warning: Class "Drupal\Core\Http\KernelEvent" not found in /var/www/html/vendor/drupal/core/includes/bootstrap.inc on line 135

Fatal error: Uncaught Error: Class "Symfony\Component\EventDispatcher\Event" not found in /var/www/html/vendor/drupal/core/lib/Drupal/Component/EventDispatcher/Event.php:15 Stack trace: #0 /var/www/html/vendor/composer/ClassLoader.php(576): include() #1 /var/www/html/vendor/composer/ClassLoader.php(427): Composer\Autoload\{closure}('/var/www/html/v...') #2 /var/www/html/vendor/drupal/core/lib/Drupal/Core/Http/KernelEvent.php(20): Composer\Autoload\ClassLoader->loadClass('Drupal\\Componen...') #3 /var/www/html/vendor/composer/ClassLoader.php(576): include('/var/www/html/v...') #4 /var/www/html/vendor/composer/ClassLoader.php(427): Composer\Autoload\{closure}('/var/www/html/v...') #5 [internal function]: Composer\Autoload\ClassLoader->loadClass('Drupal\\Core\\Htt...') #6 /var/www/html/vendor/drupal/core/includes/bootstrap.inc(135): class_alias('Drupal\\Core\\Htt...', 'Symfony\\Compone...', true) #7 /var/www/html/vendor/composer/autoload_real.php(45): require('/var/www/html/v...') #8 /var/www/html/vendor/composer/autoload_real.php(49): {closure}('2f69d3914119f04...', '/var/www/html/v...') #9 /var/www/html/vendor/autoload.php(25): ComposerAutoloaderInit53591a0dcfb0444605a3fe11287fe0b6::getLoader() #10 /var/www/html/autoload.php(16): require('/var/www/html/v...') #11 /var/www/html/index.php(14): require_once('/var/www/html/a...') #12 {main} thrown in /var/www/html/vendor/drupal/core/lib/Drupal/Component/EventDispatcher/Event.php on line 15