Contao\CoreBundle\Framework\ContaoFramework::validateInstallation PHP Method

    private function validateInstallation()
    {
        if (null === $this->request) {
            return;
        }
        /** @var Config $config */
        $config = $this->getAdapter(Config::class);
        // Show the "incomplete installation" message
        if (!$config->isComplete()) {
            throw new IncompleteInstallationException('The installation has not been completed. Open the Contao install tool to continue.');
        }
    }