if (candidates == null || candidates.isEmpty()) return Collections.emptyList();
    private static List<Integer> getPurgedConversations(Mailbox mbox, Set<Integer> candidates) throws ServiceException {        Connection conn = mbox.getOperationConnection();        List<Integer> purgedConvs = new ArrayList<Integer>();        PreparedStatement stmt = null;        ResultSet rs = null;        try {            stmt = conn.prepareStatement("SELECT id FROM " + getMailItemTableName(mbox) +                        " WHERE " + IN_THIS_MAILBOX_AND + "id IN" + DbUtil.suitableNumberOfVariables(candidates) + "AND size <= 0");            int pos = 1;            if (!DebugConfig.disableMailboxGroup)                stmt.setInt(pos++, mbox.getId());            for (int candidate : candidates)                stmt.setInt(pos++, candidate);            rs = stmt.executeQuery();            while (rs.next())                purgedConvs.add(rs.getInt(1));            return purgedConvs;        } catch (SQLException e) {            throw ServiceException.FAILURE("getting list of purged conversations", e);        } finally {            DbPool.closeResults(rs);            DbPool.closeStatement(stmt);        }    }