diff --git a/yt_dlp/utils/_utils.py b/yt_dlp/utils/_utils.py
index b5e1e2950..e00c75f6a 100644
--- a/yt_dlp/utils/_utils.py
+++ b/yt_dlp/utils/_utils.py
@@ -5120,6 +5120,9 @@ def __init__(self, extension, /):
 
     @classmethod
     def sanitize_extension(cls, extension, /, *, prepend=False):
+        if extension is None:
+            return None
+
         if '/' in extension or '\\' in extension:
             raise cls(extension)