public function setProvideRouteAlternatives($provideRouteAlternatives = null)
    {
        if (!is_bool($provideRouteAlternatives) && ($provideRouteAlternatives !== null)) {
            throw DirectionsException::invalidDirectionsRequestProvideRouteAlternatives();
        }

        $this->provideRouteAlternatives = $provideRouteAlternatives;
    }