See example at https://www.wikidata.org/wiki/Wikidata:WikiProject_PCC_Wikidata_Pilot/Northwestern_University_Libraries/Alumni_property_dashboard : a non-sense value T2202693931 is used as grouping for "unknown value" grouping.
This also results in a straight crash when grouping_link is set − see eg https://www.wikidata.org/wiki/Wikidata:WikiProject_Video_games/Statistics/Country_of_origin
The groupings query is https://w.wiki/wVm and returns items such as https://www.wikidata.org/wiki/Q61976205 which have P495=Unknown value
Triggering an update results with
<class 'pywikibot.exceptions.InvalidTitle'> 'T2157987814' is not a valid item page title
web_1 | self.process_page(page) web_1 | File "/code/integraality/pages_processor.py", line 116, in process_page web_1 | output = stats.retrieve_and_process_data() web_1 | File "/code/integraality/property_statistics.py", line 614, in retrieve_and_process_data web_1 | text += self.make_stats_for_one_grouping(grouping, item_count, higher_grouping) web_1 | File "/code/integraality/property_statistics.py", line 543, in make_stats_for_one_grouping web_1 | group_item = pywikibot.ItemPage(self.repo, grouping) web_1 | File "/usr/local/lib/python3.7/site-packages/pywikibot/page/__init__.py", line 4694, in __init__ web_1 | super(ItemPage, self).__init__(site, title, ns=ns) web_1 | File "/usr/local/lib/python3.7/site-packages/pywikibot/page/__init__.py", line 4392, in __init__ web_1 | self._link.title) web_1 | File "/usr/local/lib/python3.7/site-packages/pywikibot/page/__init__.py", line 4095, in __init__ web_1 | % (self.id, self.entity_type)) web_1 | pywikibot.exceptions.InvalidTitle: 'T2157920837' is not a valid item page title