How to fetch un-Invoiced Delivery notes for sales order – D365 Finance and Operations

So here is another code snippet, that I develop after two hours of testing and understanding the D365 F&O that get all non invoiced , delivery notes or packingslip. I want to restrict the code to invoice against Delivery note, If no non posted delivery note exists, Code will not generate the invoice.

 public static str getUninvoicedPackingSlipsBySalesId(SalesId _salesId)
 {
     CustPackingSlipJour custPackingSlipJour;    // Packing slip journal
     InventTrans         inventTrans;            // Inventory transaction

     str packingSlipIds = "";
     container distinctPackingSlips;             // Container to store unique Packing Slip IDs
     int i = 0;

     // Fetch only un-invoiced Packing Slips based on Sales ID
     while select inventTrans
     where inventTrans.InvoiceId == ""
     
     join custPackingSlipJour
     where custPackingSlipJour.PackingSlipId == inventTrans.PackingSlipId
       && custPackingSlipJour.SalesId == _salesId
     {
         // Check if the Packing Slip ID is already in the container
         if (conFind(distinctPackingSlips, custPackingSlipJour.PackingSlipId) == 0)
         {
             distinctPackingSlips += custPackingSlipJour.PackingSlipId;  // Add to container if unique
                          
         }
     }

     return con2Str(distinctPackingSlips);  // Return the comma-separated string or empty if none found
 }