public static PwObjectPoolEx FromGroup(PwGroup pg)
        {
            PwObjectPoolEx p = new PwObjectPoolEx();

            if (pg == null)
            {
                Debug.Assert(false); return(p);
            }

            ulong uFreeId = 2;             // 0 = "not found", 1 is a hole

            p.m_dUuidToId[pg.Uuid] = uFreeId;
            p.m_dIdToItem[uFreeId] = pg;
            uFreeId += 2;             // Make hole

            p.AddGroupRec(pg, ref uFreeId);
            return(p);
        }