private function _getInvalidExtensions($moduleId)
    {
        $extendedShopClasses = $this->getModuleExtensions($moduleId);
        $invalidModuleClasses = [];

        foreach ($extendedShopClasses as $extendedShopClass => $moduleClasses) {
            foreach ($moduleClasses as $moduleClass) {
                if (\OxidEsales\Eshop\Core\NamespaceInformationProvider::isNamespacedClass($moduleClass)) {
                    /** @var \Composer\Autoload\ClassLoader $composerClassLoader */
                    $composerClassLoader = include VENDOR_PATH . 'autoload.php';
                    if (!$composerClassLoader->findFile($moduleClass)) {
                        $invalidModuleClasses[$extendedShopClass][] = $moduleClass;
                    }
                } else {
                    /** Note: $aDeletedExt is passed by reference */
                    $this->backwardsCompatibleGetInvalidExtensions($moduleClass, $invalidModuleClasses, $extendedShopClass);
                }
            }
        }

        return $invalidModuleClasses;
    }