fix: Default Series in naming series patch (#15656)

diff --git a/erpnext/patches/v11_0/refactor_naming_series.py b/erpnext/patches/v11_0/refactor_naming_series.py
index 1e4a53c..428e2c3 100644
--- a/erpnext/patches/v11_0/refactor_naming_series.py
+++ b/erpnext/patches/v11_0/refactor_naming_series.py
@@ -128,5 +128,6 @@
 	return series_to_preserve
 
 def get_default_series(doctype):
-	default_series = (frappe.get_meta(doctype).get_field("naming_series").default or "")
+	field = frappe.get_meta(doctype).get_field("naming_series")
+	default_series = field.get('default', '') if field else ''
 	return default_series
\ No newline at end of file