Successors pointing to null

[yohanboniface]

Traceback (most recent call last):
  File "/home/ybon/.virtualenvs/geozone/bin/addok", line 11, in <module>
    sys.exit(main())
  File "/home/ybon/.virtualenvs/geozone/lib/python3.6/site-packages/addok/bin/__init__.py", line 30, in main
    args.func(args)
  File "/home/ybon/.virtualenvs/geozone/lib/python3.6/site-packages/addok/shell.py", line 478, in invoke
    cmd.loop()
  File "/home/ybon/.virtualenvs/geozone/lib/python3.6/site-packages/addok/shell.py", line 74, in loop
    self.cmdloop()
  File "/usr/lib64/python3.6/cmd.py", line 138, in cmdloop
    stop = self.onecmd(line)
  File "/usr/lib64/python3.6/cmd.py", line 216, in onecmd
    return self.default(line)
  File "/home/ybon/.virtualenvs/geozone/lib/python3.6/site-packages/addok/shell.py", line 66, in default
    return self.do_SEARCH(line)
  File "/home/ybon/.virtualenvs/geozone/lib/python3.6/site-packages/addok/shell.py", line 196, in do_SEARCH
    self._search(query)
  File "/home/ybon/.virtualenvs/geozone/lib/python3.6/site-packages/addok/shell.py", line 166, in _search
    results = helper(query, lat=lat, lon=lon, **filters)
  File "/home/ybon/.virtualenvs/geozone/lib/python3.6/site-packages/addok/core.py", line 169, in __call__
    return self.render()
  File "/home/ybon/.virtualenvs/geozone/lib/python3.6/site-packages/addok/core.py", line 183, in render
    self.convert()
  File "/home/ybon/.virtualenvs/geozone/lib/python3.6/site-packages/addok/core.py", line 230, in convert
    processor(self, result)
  File "/home/ybon/Code/py/addok-geozones/addok_geozones/utils.py", line 32, in follow_successor
    successor = Result.from_id(id)
  File "/home/ybon/.virtualenvs/geozone/lib/python3.6/site-packages/addok/core.py", line 107, in from_id
    return Result(dbkeys.document_key(_id))
  File "/home/ybon/.virtualenvs/geozone/lib/python3.6/site-packages/addok/core.py", line 35, in __init__
    self.load(_id)
  File "/home/ybon/.virtualenvs/geozone/lib/python3.6/site-packages/addok/core.py", line 45, in load
    raise ValueError('id "{}" not found'.format(doc_or_id[2:]))
ValueError: id "fr:commune:27049@2016-01-01" not found

When searching for "épinay" with latest dataset.
Having a quick look at it, it seems that the bug appears because some city have a successor which has a successor itself, so the first target does not exist in the dataset.
I'll work around for now, to prevent a crash.

cc @davidbgk

[yohanboniface]

Added a log:
Unable to find successor fr:commune:27049@2016-01-01 from id fr:commune:27221@1942-01-01
Unable to find successor fr:commune:61324@2016-01-01 from id fr:commune:61155@1942-01-01