Getting an empty space when trying to use gmaps4rails

So I followed the tutorial and screencast but can't seem to get this to work. I can see the div id's called map container and gmaps4rails_map where presumably, the map is supposed to be but nothing else.

I put in the yield :head and yield :script in the header and footer of the application layout view and @charger = Charger.all.to_gmaps4rails (Charger is my model) in the chargers_helper.html.erb file (I want to use in User show view).

I also put <%= gmaps4rails(@charger) %> in the show.html.erb view.

How do I get this to work?

-Update-

I just got it to work. To fix the problem I put in the @charger = ... code in a method in the helper and called the method instead of @charger.

Now the map shows up but I still cannot see the insert new marker code like in 开发者_如何学JAVAthe screencast - I don't need it for my app but am curious as to what happened to it.

In the screencast, I create model + controller with a scaffold generator. That's why I have ready to use links.

Besides, I create buttons during the screencast. Nothing is made behind the scene: the whole app is created from scratch :)