code: public UUID registerIfUnknown(final Object object) {
          final Optional<UUID> id = getId(object);
          if (!id.isPresent()) {
              return registerObject(object);
          }
          return id.get();
      }
docs: Registers an object in the meta model if it is not already registered.
  
  @param object
  The object to register.
  @return The id of the object. It doesn't matter if the object was just registered or already known.