@Override
        protected <T extends ExternalizableGraphElement> T processLoadedGraphElement(T element) {
          // by contract interner must return the element of exactly the same type
          //noinspection unchecked
          return (T)elementInterner.apply(super.processLoadedGraphElement(element));
        }
@Override
        protected <T extends ExternalizableGraphElement> T processLoadedGraphElement(T element)