Make explicit that forceFormat is optional

lib/cartodb/controllers/named_maps.js

@@ -89,7 +89,7 @@ NamedMapsController.prototype.register = function(app) {
     );
 };
 
-NamedMapsController.prototype.getNamedMapProvider = function ({ label, forcedFormat }) {
+NamedMapsController.prototype.getNamedMapProvider = function ({ label, forcedFormat = null }) {
     return function getNamedMapProviderMiddleware (req, res, next) {
         const { user } = res.locals;
         const { config, auth_token } = req.query;