docs: public Object getObjectReference(String field, String schemaName) {
          List<String> instanceIds = references.get(field);
          if(instanceIds == null || instanceIds.size() == 0) {
              return null;
          }
          String instanceId = instanceIds.get(0);
          if(instanceId == null) {
              return null;
          }
          BeanId id = BeanId.create(instanceId, schemaName);
          Object instance = instances.get(id);
          if(instance != null) {
              return instance;
          }
          instance = cache.get(id);
          instances.put(id, instance);
          return instance;
      }