query: SELECT ?item ?group ?district ?start ?end ?election
  WHERE 
  {
    ?item p:P39 ?ps .
    ?ps ps:P39 wd:Q1939555 ; pq:P2937 wd:Q30579723 .
    OPTIONAL { ?ps pq:P580 ?start }
    OPTIONAL { ?ps pq:P582 ?end }
    OPTIONAL { ?ps pq:P4100 ?group }
    OPTIONAL { ?ps pq:P768 ?district }
    OPTIONAL { ?ps pq:P2715 ?election }
  }