unapply (handler, unapplyFunction) {
    handler && handler.handleHistoryEvent(HistoryEventTypes.BEFORE_UNAPPLY, this)
    unapplyFunction()
    handler && handler.handleHistoryEvent(HistoryEventTypes.AFTER_UNAPPLY, this)
  }
@param {module:history.HistoryEventHandler} handler
@param {callback} unapplyFunction
@returns {void}