@Override
    public Optional<RowMapper<?>> build(Type type, ConfigRegistry config) {
        return Optional.of(type)
            .filter(t -> getErasedType(t) == Optional.class)
            .flatMap(t -> create(t, config));
    }
Row mapper factory which knows how to map row elements wrapped in an Optional.
core/src/main/java/org/jdbi/v3/core/mapper/OptionalRowMapperFactory.java