@Override
protected TypeIdResolver idResolver(MapperConfig<?> config, JavaType baseType,
                                    PolymorphicTypeValidator subtypeValidator, Collection<NamedType> subtypes,
                                    boolean forSer, boolean forDeser) {
    if (_idType == null) {
        throw new IllegalStateException("Can not build, 'init()' not yet called");
    }

    return new NsTypeIdResolver(baseType, config.getTypeFactory(), basicMetaData);
}