}
    public void preModify(Map context, String attrName, Object value,            Map attrsToModify, Entry entry, boolean isCreate) throws ServiceException {        String[] pool;                if (value instanceof String)            pool = new String[] { (String) value };        else if (value instanceof String[])            pool = (String[]) value;        else             throw ServiceException.INVALID_REQUEST(Provisioning.A_zimbraMailHostPool+" not a String or String[]", null);        Provisioning prov = Provisioning.getInstance();        for (int i=0; i < pool.length; i++)             if (prov.getServerById(pool[i]) == null)                    throw ServiceException.INVALID_REQUEST("specified "+Provisioning.A_zimbraMailHostPool+" does not correspond to a valid server: "+pool[i], null);    }