Move order line is Issue for a delivery id.

Hi  Team,

I'm using below queries for fetching the delivery id, But very few cases it's coming null . So we are facing a big problem to find out the root cause.

At what case move order line id will be null even though Delivery id is available.......... ?

My concern is if there is source_line_id there should be move order line id ..

select  wnd.delivery_id, wnd.name,mmt.pick_slip_number,mmt.move_order_line_id,wdd.source_line_id
       -- INTO p_scf_delivery_id, p_scf_del_name
        FROM    apps.wsh_delivery_assignments wda,
          apps.wsh_delivery_details wdd,