code: public Collection<Object> getObjectReferenceList(String field, String schemaName) {
          List<String> instanceIds = references.get(field);
          if(instanceIds == null || instanceIds.size() == 0) {
              return null;
          }
          List<Object> objects = new ArrayList<>();
          for (String instanceId : instanceIds) {
              BeanId id = BeanId.create(instanceId, schemaName);
              Object instance = instances.get(id);
              if(instance != null) {
                  objects.add(instance);
              } else {
                  instance = cache.get(id);
                  instances.put(id, instance);
                  objects.add(instance);
              }
          }
          return objects;
      }
docs: '
  Called by a proxy to lookup a list of object references. The proxy knows
  the schema name so the hold does not need to bother storing it.