How to fetch record with multi condition and sort by desc

How to fetch record with multi condition and sort by desc

I would like to create a serial number; the code is by year and month: [YYMMXXXX], XXXX is from 0001 to 9999.
I create two fields as condition of filter, the Deluge code is:
  2. if(SerialNo == "")
  3. {
  4. CurrentYear = zoho.currentdate.getYear();
  5. CurrentMonth = zoho.currentdate.getMonth();
  6. query_map = Map();
  7. query_map.put("Create_Year",CurrentYear);
  8. query_map.put("Create_Month",CurrentMonth);
  9. query_map.put("sort_by","Serial_No");
  10. query_map.put("sort_order","desc");
  11. RecRequest2 = zoho.crm.getRecords("Request",1,5,query_map);
  12. if(RecRequest2.size() > 1)
  13. {
  14. NewSerialNo = RecRequest2.get(1).get("Ticket_No").toLong() + 1RecRequest2.get(1).get("Ticket_No").toLong() + 1;
  15. }
  16. else
  17. {
  18. NewSerialNo = CurrentYear.toString() + CurrentMonth.toString() + "0001";
  19. }
  20. }
The "query_map" with two condition: create year and month, but the "RecRequest2" are not including the condition, the result of Create Year and Create Month is empty. 
How can I fix it?