getRssUrl(options) {
        let rssUrl = null;

        const collectionIndexRouter = _.find(routers, {name: 'CollectionRouter', routerName: 'index'});

        if (collectionIndexRouter) {
            rssUrl = collectionIndexRouter.getRssUrl(options);

            // CASE: is rss enabled?
            if (rssUrl) {
                return rssUrl;
            }
        }

        const collectionRouters = _.filter(routers, {name: 'CollectionRouter'});

        if (collectionRouters && collectionRouters.length === 1) {
            rssUrl = collectionRouters[0].getRssUrl(options);

            // CASE: is rss enabled?
            if (rssUrl) {
                return rssUrl;
            }
        }

        return rssUrl;
    }
@description Helper to figure out the primary rss url.

If you either configure multiple collections or your collection does not live on "/", we need to know
what your primary rss url is, otherwise /rss could be 404.

More context: https://github.com/TryGhost/Team/issues/65#issuecomment-393622816

@param {Object} options
@returns {String}