message: fix calculation of realm intersections
  don't return an empty nested array
diff: @@ -182,7 +182,7 @@ function mayReadLessThanAllFields(grant) {
  function realmIntersections(choiceRealms, singleRealms) {
  let nextChoices = choiceRealms[0];
  if (!nextChoices) {
  - return [singleRealms];
  + return singleRealms.length > 0 ? [singleRealms] : [];
  }
  let rest = realmIntersections(choiceRealms.slice(1), singleRealms);
  return nextChoices.map(choice => rest.concat([choice]));
  