code: ITypedReferenceableInstance getDuringWalk(Id id, ObjectGraphWalker walker) throws RepositoryException {
          ClassStore cS = getClassStore(id.getTypeName());
          if (cS == null) {
              throw new RepositoryException(String.format("Unknown Class %s", id.getTypeName()));
          }
          cS.validate(this, id);
          ReferenceableInstance r = cS.createInstance(this, id);
          cS.load(r);
          for (String traitName : r.getTraits()) {
              HierarchicalTypeStore tt = typeStores.get(traitName);
              tt.load(r);
          }
  
          walker.addRoot(r);
          return r;
      }
docs: /*
  - Id must be valid; Class must be valid.
  - Ask ClassStore to createInstance.
  - Ask ClassStore to load instance.
  - load instance traits
  - add to GraphWalker