         if xhr.status == 200
           client = @currentEntityFollowingProxyClient(res.id, options)
           @entity_mapping[entity] = client
-          callback(client)
+          callback?(client)
         else
           @fetch(params, callback, _.extend(options, {skip_following_check: true}))
 

    return unless (entity = params.entity)

    if client = @entity_mapping[entity]
      callback(client)
      return client

    unless (options.hasOwnProperty('fetch') && !options.fetch)

          middleware: [].concat(@middleware.tent)
        }, options.client_options)
        @entity_mapping[entity] = client
        return callback?(client)

    client = new HTTP.Client _.extend({
      hosts: [TentStatus.config.tent_proxy_root + "/#{encodeURIComponent entity}"]
