Make vendor nullable

internal/processor/purchase_order_processor.go

@@ -55,10 +55,12 @@ func NewPurchaseOrderProcessorImpl(
 }
 
 func (p *PurchaseOrderProcessorImpl) CreatePurchaseOrder(ctx context.Context, organizationID uuid.UUID, req *models.CreatePurchaseOrderRequest) (*models.PurchaseOrderResponse, error) {
-	// Check if vendor exists and belongs to organization
-	_, err := p.vendorRepo.GetByIDAndOrganizationID(ctx, req.VendorID, organizationID)
-	if err != nil {
-		return nil, fmt.Errorf("vendor not found: %w", err)
+	// Check if vendor exists and belongs to organization when provided.
+	if req.VendorID != nil {
+		_, err := p.vendorRepo.GetByIDAndOrganizationID(ctx, *req.VendorID, organizationID)
+		if err != nil {
+			return nil, fmt.Errorf("vendor not found: %w", err)
+		}
 	}
 
 	// Check if PO number already exists in organization
@@ -186,7 +188,7 @@ func (p *PurchaseOrderProcessorImpl) UpdatePurchaseOrder(ctx context.Context, id
 		if err != nil {
 			return nil, fmt.Errorf("vendor not found: %w", err)
 		}
-		poEntity.VendorID = *req.VendorID
+		poEntity.VendorID = req.VendorID
 	}
 
 	// Check if PO number already exists (if PO number is being updated)