fix(einvoicing): service item check (#26010)

diff --git a/erpnext/regional/india/e_invoice/utils.py b/erpnext/regional/india/e_invoice/utils.py
index a1179ff..0eaf790 100644
--- a/erpnext/regional/india/e_invoice/utils.py
+++ b/erpnext/regional/india/e_invoice/utils.py
@@ -199,7 +199,7 @@
 
 		item.batch_expiry_date = frappe.db.get_value('Batch', d.batch_no, 'expiry_date') if d.batch_no else None
 		item.batch_expiry_date = format_date(item.batch_expiry_date, 'dd/mm/yyyy') if item.batch_expiry_date else None
-		item.is_service_item = 'Y' if item.gst_hsn_code[:2] == "99" else 'N'
+		item.is_service_item = 'Y' if item.gst_hsn_code and item.gst_hsn_code[:2] == "99" else 'N'
 		item.serial_no = ""
 
 		item = update_item_taxes(invoice, item)