query: PREFIX wd: <http://www.wikidata.org/entity/>
  PREFIX wdt: <http://www.wikidata.org/prop/direct/>
  PREFIX wikibase: <http://wikiba.se/ontology#>
  PREFIX p: <http://www.wikidata.org/prop/>
  PREFIX v: <http://www.wikidata.org/prop/statement/>
  PREFIX q: <http://www.wikidata.org/prop/qualifier/>
  PREFIX rdfs: <http://www.w3.org/2000/01/rdf-schema#>
  
  SELECT ?h WHERE {
     ?h wdt:P1343 wd:Q17166797 .
     OPTIONAL {?h wdt:P2332 ?d } 
     FILTER (!bound(?d))
   }