     })
     @
 
-  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.


    len

  ###
    All items will appear to be stale when fetching with `.objectAt`.

    @method expire
    @chainable
  ###
  expire: ->
    set(@, 'expired', Date.now())
    @

  ###
    Empty the sparse data. (The "nuclear option.")

    @method reset
    @chainable
