From 854881bba258378ba90c3f9de29496c5fd650d16 Mon Sep 17 00:00:00 2001
From: Richard Harrison <rjh@zaretto.com>
Date: Mon, 4 Dec 2017 07:30:48 +0100
Subject: [PATCH] Prevent nullptr exception. Had this happen once.

---
 simgear/canvas/elements/CanvasGroup.cxx | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/simgear/canvas/elements/CanvasGroup.cxx b/simgear/canvas/elements/CanvasGroup.cxx
index c753c2e2..d398fe2e 100644
--- a/simgear/canvas/elements/CanvasGroup.cxx
+++ b/simgear/canvas/elements/CanvasGroup.cxx
@@ -387,7 +387,9 @@ namespace canvas
     OSGUserData* ud =
       static_cast<OSGUserData*>(_transform->getChild(index)->getUserData());
     assert(ud);
-    return ud->element;
+    if (ud)
+        return ud->element;
+    return nullptr;
   }
 
   //----------------------------------------------------------------------------