     })
     @
 
-  isExpiredAt: (timestamp) ->
+  isExpiredAt: (timestamp = 0) ->
     return false if get(@, 'is_loading')
     !!(get(@, 'is_stale') or get(@, 'last_fetched_at') <= timestamp)
 

  ###
    @private

    Prepare to fetch the total number of available objects from the
    persistence layer.


    result = get(@, @_pathForIndex(idx)) ? @insertSparseArrayItem(idx)
    if (result and result.isExpiredAt(get(@, 'expired')) isnt true)
      return result
    @_requestObjectAt(idx, dontFetch)

  ###
    Fetches data regarding the total number of objects in the
