query: #Check that every public library  has an (optional) image
  SELECT DISTINCT ?item ?itemLabelNL ?image  
  WHERE 
  {
    ?item (p:P31/ps:P31) wd:Q28564,wd:Q11396180;wdt:P17 wd:Q55.  #public library #library branch #from the Netherlands 
    OPTIONAL{?item wdt:P18 ?image.} #image P18
    OPTIONAL{?item rdfs:label ?itemLabelNL FILTER(LANG(?itemLabelNL)='nl').}
  }
  ORDER BY ?item