From cca78e0601a128883571f218a81ba5266875caad Mon Sep 17 00:00:00 2001
From: tcavallari <tommaso@tommasocavallari.com>
Date: Tue, 21 Apr 2015 10:08:17 +0200
Subject: [PATCH] Null Pointer check in vizimpl.cpp

Should fix #4191 (http://code.opencv.org/issues/4191)
---
 modules/viz/src/vizimpl.cpp | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/modules/viz/src/vizimpl.cpp b/modules/viz/src/vizimpl.cpp
index ab621ad16..b2ec7603f 100644
--- a/modules/viz/src/vizimpl.cpp
+++ b/modules/viz/src/vizimpl.cpp
@@ -85,7 +85,7 @@ void cv::viz::Viz3d::VizImpl::TimerCallback::Execute(vtkObject* caller, unsigned
 
 void cv::viz::Viz3d::VizImpl::ExitCallback::Execute(vtkObject*, unsigned long event_id, void*)
 {
-    if (event_id == vtkCommand::ExitEvent)
+    if (event_id == vtkCommand::ExitEvent && viz->interactor_)
     {
         viz->interactor_->TerminateApp();
         viz->interactor_ = 0;