From 0e21058d10959013ae85bcc9e69a2db6536ddcfb Mon Sep 17 00:00:00 2001
From: Robert Osfield <robert@openscenegraph.com>
Date: Thu, 23 Jun 2016 17:58:35 +0100
Subject: [PATCH] Added check against null

---
 src/osgUtil/Optimizer.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/osgUtil/Optimizer.cpp b/src/osgUtil/Optimizer.cpp
index 813872986..b6c942c6b 100644
--- a/src/osgUtil/Optimizer.cpp
+++ b/src/osgUtil/Optimizer.cpp
@@ -3218,7 +3218,7 @@ void Optimizer::FlattenBillboardVisitor::process()
             mergeAcceptable = false;
         }
 
-        if (mergeAcceptable)
+        if (mergeAcceptable && mainGroup)
         {
             osg::Billboard* new_billboard = new osg::Billboard;
             new_billboard->setMode(billboard->getMode());