protected function ensureFileIsReadable()
    {
        $filePath = $this->filePath;
        if (!is_readable($filePath) || !is_file($filePath)) {
            throw new InvalidArgumentException(sprintf(
                'Dotenv: Environment file .env not found or not readable. '.
                'Create file with your environment settings at %s',
                $filePath
            ));
        }
    }