use xaggs to make graphics

[enu...@gmail.com]

It is impossible for me to make a graph using xaggs functions like historical_avg.
If I use [[hist]]
              [[[outtemp]]]
                   aggregation_type = historical_avg
                   aggregation_interval = day

I get the error

Dec  9 18:56:00 raspberrypi weewx[20140] ERROR weewx.reportengine: Caught unrecoverable exception in generator 'weewx.imagegenerator.ImageGenerator'
Dec  9 18:56:00 raspberrypi weewx[20140] ERROR weewx.reportengine:         ****  ('outTemp', (1638982800, 1639080000), <weewx.manager.DaySummaryManager object at 0xb1e3ba90>, None, None)
Dec  9 18:56:00 raspberrypi weewx[20140] ERROR weewx.reportengine:         ****  Traceback (most recent call last):
Dec  9 18:56:00 raspberrypi weewx[20140] ERROR weewx.reportengine:         ****    File "/usr/share/weewx/weewx/reportengine.py", line 196, in run
Dec  9 18:56:00 raspberrypi weewx[20140] ERROR weewx.reportengine:         ****      obj.start()
Dec  9 18:56:00 raspberrypi weewx[20140] ERROR weewx.reportengine:         ****    File "/usr/share/weewx/weewx/reportengine.py", line 281, in start
Dec  9 18:56:00 raspberrypi weewx[20140] ERROR weewx.reportengine:         ****      self.run()
Dec  9 18:56:00 raspberrypi weewx[20140] ERROR weewx.reportengine:         ****    File "/usr/share/weewx/weewx/imagegenerator.py", line 41, in run
Dec  9 18:56:00 raspberrypi weewx[20140] ERROR weewx.reportengine:         ****      self.genImages(self.gen_ts)
Dec  9 18:56:00 raspberrypi weewx[20140] ERROR weewx.reportengine:         ****    File "/usr/share/weewx/weewx/imagegenerator.py", line 181, in genImages
Dec  9 18:56:00 raspberrypi weewx[20140] ERROR weewx.reportengine:         ****      aggregate_interval=aggregate_interval)
Dec  9 18:56:00 raspberrypi weewx[20140] ERROR weewx.reportengine:         ****    File "/usr/share/weewx/weewx/xtypes.py", line 99, in get_series
Dec  9 18:56:00 raspberrypi weewx[20140] ERROR weewx.reportengine:         ****      raise weewx.UnknownType(obs_type, timespan, db_manager, aggregate_type, aggregate_interval)
Dec  9 18:56:00 raspberrypi weewx[20140] ERROR weewx.reportengine:         ****  weewx.UnknownType: ('outTemp', (1638982800, 1639080000), <weewx.manager.DaySummaryManager object at 0xb1e3ba90>, None, None)
Dec  9 18:56:00 raspberrypi weewx[20140] ERROR weewx.reportengine:         ****  Generator terminated

If I remove aggregaton_interval then I get a message telling me that I need to define an interval.
If I just use [[[history_avg]]] to draw the graph I get the same error as before.