protected function useExoticConfigFile()
    {
        try {
            $configPath = $this->paths()->getAbsolutePath($this->input->getOption('config'));
            if ($configPath !== $this->paths()->getDefaultConfigPath()) {
                return $this->paths()->getRelativeProjectPath($configPath);
            }
        } catch (FileNotFoundException $e) {
            // no config file should be set.
        }

        return null;
    }