presto-spi/src/main/java/io/prestosql/spi/resourcegroups/ResourceGroupId.java/ResourceGroupId/getParent
class ResourceGroupId:    public Optional<ResourceGroupId> getParent()
    {
        if (segments.size() == 1) {
            return Optional.empty();
        }
        return Optional.of(new ResourceGroupId(segments.subList(0, segments.size() - 1)));
    }