From 6a036fefd9e842ad46b1c42b79f2c08b530dca64 Mon Sep 17 00:00:00 2001
From: Ard <88337265+aw471@users.noreply.github.com>
Date: Mon, 2 Nov 2026 14:14:21 -0800
Subject: [PATCH] Avoid scalar extraction when compacting empty ragged tensors

---
 sdm/tensor/var_len.py | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/sdm/tensor/var_len.py b/sdm/tensor/var_len.py
index a31438a97..5ff52d9aa 100644
--- a/sdm/tensor/var_len.py
+++ b/sdm/tensor/var_len.py
@@ -1473,6 +1473,8 @@ def _from_layout_view(inp: VarLenTensor, view: Tensor) -> VarLenTensor:
 
 
 def _compact(start: Tensor, end: Tensor) -> tuple[Tensor, Tensor]:
+    if start.numel() == 0:
+        return start.new_zeros(1), start.new_empty(0)
     count = end - start
 
     offset = count.new_empty(count.numel() + 1, dtype=torch.int64)