fetch customer_gstin or billing_address_gstin optionally (#14075)

diff --git a/erpnext/regional/report/gstr_1/gstr_1.py b/erpnext/regional/report/gstr_1/gstr_1.py
index a14500a..52f0748 100644
--- a/erpnext/regional/report/gstr_1/gstr_1.py
+++ b/erpnext/regional/report/gstr_1/gstr_1.py
@@ -23,7 +23,7 @@
 			posting_date,
 			base_grand_total,
 			base_rounded_total,
-			customer_gstin,
+			COALESCE(NULLIF(customer_gstin,''), NULLIF(billing_address_gstin, '')) as customer_gstin,
 			place_of_supply,
 			ecommerce_gstin,
 			reverse_charge,