Backbone Collection with subModels using backbone-relational (not working)

sites.coffee

Dashboard.module 'Entities', (Entities, Dashboard, Backbone, Marionette, $, _) ->
  class Entities.Site extends Backbone.RelationalModel
    relations: [
      {
        type: Backbone.HasMany
        key: 'widgets'
        relatedModel: 'Dashboard.Entities.Widget'
        parse: true
        relatedCollection: 'Dashboard.Entities.WidgetCollection'
        reverseRelation: {
          key: 'site'
          includeInJSON: Backbone.Model.prototype.idAttribute
        }
      }
    ]

  class Entities.SiteCollection extends Backbone.Collection
    url: '/dashboard.json'
    model: Entities.Site

widget.coffee

Dashboard.module 'Entities', (Entities, Dashboard, Backbone, Marionette, $, _) ->
  class Entities.Widget extends Backbone.RelationalModel
    subModelTypes:
      'numbers': 'Entities.NumbersWidget'

  Entities.Widget.setup()

  class Entities.NumbersWidget extends Entities.Widget

  class Entities.WidgetCollection extends Backbone.Collection
    model: Entities.Widget