Greater than Zero values not retruned in PLSQL function

Hi ,

We have the requirement to get the( subinventory is null and QTY>0).

But the QTY has been returned from PLSQL function.

Hence when we declare the condition it is not working.

SELECT DISTINCT msib.segment1,

msib.description,

 hrou.NAME,

nvl(null,0)item_cost,

msib.inventory_item_id,

 msib.organization_id,

  nvl(null,0)re_order_point,

  nvl(null,'NULL') sec_inv,

 --pda.DESTINATION_SUBINVENTORY,

 (ood.ORGANIZATION_CODE

 ||'-'

|| nvl(null,'NULL')) secondary_inventory

FROM po_headers_all pha,

 po_lines_all pla,

 -- po_releases_all    pra,

 po_line_locations_all plla,

 po_distributions_all pda,

 mtl_parameters mp,

 mtl_system_items_b msib,