query: #Wereldtentoonstelling
  SELECT ?item ?itemLabel ?PIT
  WHERE 
  {
    ?item wdt:P31 wd:Q172754 .
    ?item wdt:P790 wd:Q1010514 .
    OPTIONAl { ?item wdt:P585 ?PIT } .
    SERVICE wikibase:label { bd:serviceParam wikibase:language "[AUTO_LANGUAGE],en". }
  }
  order by asc(?PIT)