code: public void addObjectId( IdKey id, Object instance ) {
          if ( null == idToObject ) {
              idToObject = new HashMap<IdKey, Object>();
          }
          idToObject.put( id, instance );
      }
docs: <p>addObjectId</p>
  
  @param id a {@link com.fasterxml.jackson.annotation.ObjectIdGenerator.IdKey} object.
  @param instance a {@link java.lang.Object} object.