I'm not really sure if this should be able to be supported, but the error messages says to report it so I am. :-)
The error is: <class 'IndexError'> list index out of range with the following input:
{{Property dashboard
|selector_sparql=wdt:P17 wd:Q408; wdt:P31 ?type . { SELECT * WHERE { ?type wdt:P279 wd:Q7075 } }
|grouping_property=P131
|higher_grouping=wdt:P131
|properties=P625,P18,P6375
|stats_for_no_group=1
|grouping_threshold=0
|property_threshold=0
}}The idea is to select all entities of a type or any subtype (in this case, libraries and things like public libraries, academic libraries, etc.).
Another example that fails:
{{Property dashboard
|selector_sparql= p:P31 []. {?entity wdt:P69 wd:Q309350.} UNION {?entity wdt:P69 wd:Q6806876. }
|grouping_property=P21
|grouping_threshold=1
|stats_for_no_group=False
|properties=P18,Len,P244,P214,P496,P2381
}}