From d4f24402c54bf73732e17844c279123673e4d603 Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@gmail.com>
Date: Wed, 3 Aug 2016 00:10:21 +0200
Subject: [PATCH] Check for null VirtualizingPanel.

The panel may not have been created when the virtualization mode is changed - handle that. Fixes #634.
---
 src/Avalonia.Controls/Presenters/ItemVirtualizer.cs | 8 ++++++--
 1 file changed, 6 insertions(+), 2 deletions(-)

diff --git a/src/Avalonia.Controls/Presenters/ItemVirtualizer.cs b/src/Avalonia.Controls/Presenters/ItemVirtualizer.cs
index 964ce82849..ae198dc58c 100644
--- a/src/Avalonia.Controls/Presenters/ItemVirtualizer.cs
+++ b/src/Avalonia.Controls/Presenters/ItemVirtualizer.cs
@@ -185,8 +185,12 @@ namespace Avalonia.Controls.Presenters
         /// <inheritdoc/>
         public virtual void Dispose()
         {
-            VirtualizingPanel.Controller = null;
-            VirtualizingPanel.Children.Clear();
+            if (VirtualizingPanel != null)
+            {
+                VirtualizingPanel.Controller = null;
+                VirtualizingPanel.Children.Clear();
+            }
+
             Owner.ItemContainerGenerator.Clear();
         }