static <A extends Concept> A nuLike getConceptOpt(Class<A> cc, long id) {
  ret getConceptOpt(db_mainConcepts(), cc, id);
}

static <A extends Concept> A getConceptOpt(Concepts concepts, Class<A> cc, long id) {
  ret concepts == null ? null : optCast(cc, concepts.getConcept(id));
}