protected function validateStatusCode($statusCode) : void
	{
		if (! \is_int($statusCode))
		{
			throw new \InvalidArgumentException('HTTP status-code must be an integer');
		}
		else if (! ($statusCode >= 100 && $statusCode <= 599))
		{
			throw new \InvalidArgumentException(\sprintf('The given status-code "%d" is not valid', $statusCode));
		}
	}