diff --git a/nested_inline/admin.py b/nested_inline/admin.py
index a1906f5..48432e0 100644
--- a/nested_inline/admin.py
+++ b/nested_inline/admin.py
@@ -99,6 +99,8 @@ def wrap_nested_inline_formsets(self, request, inline, formset):
         media = None
 
         def get_media(extra_media):
+            if extra_media is None:
+                return ''
             if media:
                 return media + extra_media
             else: