diff --git a/scrapy/pipelines/media.py b/scrapy/pipelines/media.py
index 153047acf..a28e47d70 100644
--- a/scrapy/pipelines/media.py
+++ b/scrapy/pipelines/media.py
@@ -208,7 +208,7 @@ class MediaPipeline:
             # minimize cached information for failure
             result.cleanFailure()
             result.frames = []
-            result.stack = None
+            result.stack = []
 
             # This code fixes a memory leak by avoiding to keep references to
             # the Request and Response objects on the Media Pipeline cache.