From a1b39d5959377cb8f8aaab2a837aedddc3a2589b Mon Sep 17 00:00:00 2001
From: Saran Tunyasuvunakool <stunya@google.com>
Date: Mon, 9 Oct 2023 11:00:14 -0700
Subject: [PATCH] Fix a segfault in `simulate` on mouse scroll without a loaded
 model.

Fixes #1089

PiperOrigin-RevId: 571985561
Change-Id: I4acc7c2a6032d678023783646c3f00cfe30641f2
---
 simulate/simulate.cc | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/simulate/simulate.cc b/simulate/simulate.cc
index cb8bd4d6..d25362e3 100644
--- a/simulate/simulate.cc
+++ b/simulate/simulate.cc
@@ -1633,7 +1633,7 @@ void UiEvent(mjuiState* state) {
   // 3D scroll
   if (state->type==mjEVENT_SCROLL && state->mouserect==3) {
     // emulate vertical mouse motion = 2% of window height
-    if (!sim->is_passive_) {
+    if (sim->m_ && !sim->is_passive_) {
       mjv_moveCamera(sim->m_, mjMOUSE_ZOOM, 0, -zoom_increment*state->sy, &sim->scn, &sim->cam);
     } else {
       mjv_moveCameraFromState(