diff --git a/dvc/output.py b/dvc/output.py
index 1ddcd7a83..01cae1bca 100644
--- a/dvc/output.py
+++ b/dvc/output.py
@@ -816,6 +816,7 @@ class Output:
         else:
             return None
 
+        assert obj
         fs_path = self.fs.path
         if filter_info and filter_info != self.fs_path:
             prefix = fs_path.relparts(filter_info, self.fs_path)