private function parseEnvironmentParams($value)
    {
        // env.variable is an environment variable
        $env = explode('.', $value);
        if ('env' === $env[0]) {
            $envParam = getenv($env[1]);
            if (false === $envParam) {
                throw new InvalidArgumentException("Environment variable '$env[1]' is not defined.");
            }

            return $envParam;
        }

        return null;
    }