From 25a816b2ff20d03676e3b83b628f3926c4d65aa6 Mon Sep 17 00:00:00 2001
From: JunghwanNA <70629228+shaun0927@users.noreply.github.com>
Date: Fri, 17 Apr 2026 13:11:18 +0900
Subject: [PATCH] Normalize 'lists' argument in
 MerlinDataLoader._augment_schema

cats/conts/labels are normalized to [] when None, but lists was not.
The subsequent 'conts + cats + labels + lists' raises
TypeError: can only concatenate list (not "NoneType") to list
for any caller that omits lists=, which is the common case for
datasets without list-typed features.

Fixes #812
---
 transformers4rec/torch/utils/data_utils.py | 1 +
 1 file changed, 1 insertion(+)

diff --git a/transformers4rec/torch/utils/data_utils.py b/transformers4rec/torch/utils/data_utils.py
index db56376e31..1949564126 100644
--- a/transformers4rec/torch/utils/data_utils.py
+++ b/transformers4rec/torch/utils/data_utils.py
@@ -398,6 +398,7 @@ def _augment_schema(
         cats = cats or []
         conts = conts or []
         labels = labels or []
+        lists = lists or []
 
         schema = schema.select_by_name(conts + cats + labels + lists)