Prepares for the given region+item combo by instantiating a
        :py:class:`HistoryItemsInRegionList` instance, which will track
        region ID, type ID, and generated time. This is mostly used for
        the JSON deserialization process in case there are no orders for
        the given region+item combo.

        :param int region_id: The region ID.
        :param int type_id: The item's type ID.
        :param datetime.datetime generated_at: The time that the order set
            was generated.
        :keyword bool error_if_entries_present: If True, raise an exception if
            an entry already exists for this item+region combo when this is
            called. This failsafe may be disabled by passing False here.

def set_empty_region(self, region_id, type_id, generated_at,
                         error_if_entries_present=True):
        """
        Prepares for the given region+item combo by instantiating a
        :py:class:`HistoryItemsInRegionList` instance, which will track
        region ID, type ID, and generated time. This is mostly used for
        the JSON deserialization process in case there are no orders for
        the given region+item combo.

        :param int region_id: The region ID.
        :param int type_id: The item's type ID.
        :param datetime.datetime generated_at: The time that the order set
            was generated.
        :keyword bool error_if_entries_present: If True, raise an exception if
            an entry already exists for this item+region combo when this is
            called. This failsafe may be disabled by passing False here.
        """
        key = '%s_%s' % (region_id, type_id)
        if error_if_entries_present and self._history.has_key(key):
            raise ItemAlreadyPresentError(
                "Orders already exist for the given region and type ID. "
                "Pass error_if_orders_present=False to disable this failsafe, "
                "if desired."
            )

        self._history[key] = HistoryItemsInRegionList(
            region_id, type_id, generated_at)