From 22e30b838e1a89596be6bc5ce4bdd70f303e9c5e Mon Sep 17 00:00:00 2001
From: JunghwanNA <70629228+shaun0927@users.noreply.github.com>
Date: Fri, 17 Apr 2026 13:09:56 +0900
Subject: [PATCH] Fix Head.build raising TypeError on body without output_size

PR #802 changed the default sentinel in
getattr(self.body, "output_size", lambda: None)()
to
getattr(self.body, "output_size", None)()

When the body lacks an output_size attribute, getattr returns None,
and the trailing () evaluates None(), which raises
TypeError: 'NoneType' object is not callable. The intended
raise ValueError("Can't infer output-size...") branch below is
never reached.

Restore the original callable sentinel so control flow falls
through to the descriptive ValueError as designed.

Fixes #811
---
 transformers4rec/torch/model/base.py | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/transformers4rec/torch/model/base.py b/transformers4rec/torch/model/base.py
index 3aeb4eb3f..e187fac24 100644
--- a/transformers4rec/torch/model/base.py
+++ b/transformers4rec/torch/model/base.py
@@ -285,7 +285,7 @@ def build(self, inputs=None, device=None, task_blocks=None):
         device
         task_blocks
         """
-        if not getattr(self.body, "output_size", None)():
+        if not getattr(self.body, "output_size", lambda: None)():
             raise ValueError(
                 "Can't infer output-size of the body, please provide  "
                 "a `Block` with a output-size. You can wrap any torch.Module in a Block."