query: SELECT ?item ?unit ?exception
  WHERE
  {
  	{
        SELECT ?item ?unit
        WHERE
        {
          ?item      p:P2630              ?stmnode.
          ?stmnode   psv:P2630            ?valuenode.
          ?valuenode wikibase:quantityUnit   ?unit.
        }
      }.
      OPTIONAL {
  		wd:P2630 p:P2302 [ ps:P2302 wd:Q21514353; pq:P2303 ?exc ] .
  		FILTER( ?exc = ?item ) .
  	} .
  	BIND( BOUND( ?exc ) AS ?exception ) .
  }