Fix support for PHP8 union types

Author: nicolas-grekas

Kernel/MicroKernelTrait.php

@@ -112,7 +112,7 @@ public function registerContainerConfiguration(LoaderInterface $loader)
                 throw new \LogicException(sprintf('"%s" uses "%s", but does not implement the required method "protected function configureContainer(ContainerConfigurator $c): void".', get_debug_type($this), MicroKernelTrait::class), 0, $e);
             }
 
-            $configuratorClass = $configureContainer->getNumberOfParameters() > 0 && ($type = $configureContainer->getParameters()[0]->getType()) && !$type->isBuiltin() ? $type->getName() : null;
+            $configuratorClass = $configureContainer->getNumberOfParameters() > 0 && ($type = $configureContainer->getParameters()[0]->getType()) instanceof \ReflectionNamedType && !$type->isBuiltin() ? $type->getName() : null;
 
             if ($configuratorClass && !is_a(ContainerConfigurator::class, $configuratorClass, true)) {
                 $this->configureContainer($container, $loader);