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."