fix: dont send empty serial no in get_item_details

[skip ci]
diff --git a/erpnext/stock/get_item_details.py b/erpnext/stock/get_item_details.py
index f72588e..f83f692 100644
--- a/erpnext/stock/get_item_details.py
+++ b/erpnext/stock/get_item_details.py
@@ -167,6 +167,9 @@
 			reserved_so = get_so_reservation_for_item(args)
 			out.serial_no = get_serial_no(out, args.serial_no, sales_order=reserved_so)
 
+	if not out.serial_no:
+		out.pop("serial_no", None)
+
 
 def set_valuation_rate(out, args):
 	if frappe.db.exists("Product Bundle", args.item_code, cache=True):