Integer li_Null, li_id
SetNull(li_Null)
if dwo.name = 'id_doc_type_s' then
	if isNull(data) or Trim(data) = '' then dw_ie.object.id_doc_type[row] = li_Null
		if Trim(data) <> '' then
			SELECT id_lg
   		INTO :li_id
    		FROM sp_lg
  			WHERE Name_lg = :data ;
			if li_id >  0  then dw_ie.object.id_doc_type[row] = li_id else	MessageBox('','Несоотвествие')
	end if
end if

т.к. пока не видно команды DW.Update()