minor fix in patch for mariadb version
diff --git a/erpnext/patches/v8_1/set_delivery_date_in_so_item.py b/erpnext/patches/v8_1/set_delivery_date_in_so_item.py
index e3e23a5..2e81571 100644
--- a/erpnext/patches/v8_1/set_delivery_date_in_so_item.py
+++ b/erpnext/patches/v8_1/set_delivery_date_in_so_item.py
@@ -8,16 +8,14 @@
 		frappe.db.sql("""
 			update `tabSales Order`
 			set delivery_date = final_delivery_date
-			where (delivery_date is null or delivery_date = '' or delivery_date = '0000-00-00')
+			where (delivery_date is null or delivery_date = '0000-00-00')
 				and order_type = 'Sales'""")
 
 	frappe.db.sql("""
 		update `tabSales Order` so, `tabSales Order Item` so_item
-		set so_item.delivery_date = if(ifnull(so.delivery_date, '0000-00-00'), ifnull(so.delivery_date, '0000-00-00'), '0000-00-00')
+		set so_item.delivery_date = so.delivery_date
 		where so.name = so_item.parent
 			and so.order_type = 'Sales'
-			and (so_item.delivery_date is null or so_item.delivery_date = ''
-				or so_item.delivery_date = '0000-00-00')
-			and (so.delivery_date is not null and so.delivery_date != '' and so.delivery_date != ""
-				and so.delivery_date != '0000-00-00')
-	""")
+			and (so_item.delivery_date is null or so_item.delivery_date = '0000-00-00')
+			and (so.delivery_date is not null and so.delivery_date != '0000-00-00')
+	""")
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