static Concept nuLike getConceptOrMarkMissingObject(Concepts cc default db_mainConcepts(), Class<? extends Concept> requiredClass, long id) {
  if (cc == null) null;
  Concept c = getConcept(cc, id);
  if (isInstanceOf(c, requiredClass)) ret c;
  if (c instanceof CMissingObject) ret c;
  if (c != null) fail("Can't cast: " + toStringWithClassName(c) + "/" + requiredClass);
  
  // it's missing, create the CMissing marker
  lock dbLock(cc);
  if (getConcept(cc, id) == null)
    ret cnew(cc, CMissingObject);
    
  null;
}