Gmaps4Rails build_markers not working in javascript

I'm trying to build a markers Json with build_markers. It seems to build the hash right when I display it in the page but somehow in javascript it returns null.

javascript (not using require tree if that matters)

function initialize() {

handler = Gmaps.build('Google');
handler.buildMap({ provider: {maxZoom:17, minZoom:5}, internal: {id: 'map'}}, function(){
  markers = handler.addMarkers(<%= raw @hash.to_json %>);
  handler.bounds.extendWith(markers);

   handler.fitMapToBounds();
});

}

google.maps.event.addDomListener(window, "load", initialize);

controller

      def index
    @apartments = Apartment.all
    @hash = Gmaps4rails.build_markers(@apartments) do |apartment, marker|
      marker.lat apartment.latitude
      marker.lng apartment.longitude
    end
  end

When checking source it just shows handler.addMarkers(null)