From 8da396c518af4374658d76ce1e49e21997606323 Mon Sep 17 00:00:00 2001
From: Dan Walmsley <dan@walms.co.uk>
Date: Fri, 19 Feb 2016 11:13:09 +0000
Subject: [PATCH] fixed code that crashes mono compiler.

---
 src/Perspex.Controls/Utils/UndoRedoHelper.cs | 15 ++++++++++++---
 1 file changed, 12 insertions(+), 3 deletions(-)

diff --git a/src/Perspex.Controls/Utils/UndoRedoHelper.cs b/src/Perspex.Controls/Utils/UndoRedoHelper.cs
index 9de2ca9b35..70e5921d8d 100644
--- a/src/Perspex.Controls/Utils/UndoRedoHelper.cs
+++ b/src/Perspex.Controls/Utils/UndoRedoHelper.cs
@@ -37,7 +37,12 @@ namespace Perspex.Controls.Utils
 
         public void Undo()
         {
-            _host.UndoRedoState= (_currentNode = _currentNode?.Previous ?? _currentNode).Value;
+			if (_currentNode != null)  
+			{
+				_currentNode = _currentNode.Previous;
+			}
+
+			_host.UndoRedoState = _currentNode?.Value;            
         }
 
         public bool IsLastState => _currentNode.Next == null;
@@ -62,8 +67,12 @@ namespace Perspex.Controls.Utils
         }
 
         public void Redo()
-        {
-            _host.UndoRedoState = (_currentNode = _currentNode?.Next ?? _currentNode).Value;
+        {            
+			if (_currentNode != null) {
+				_currentNode = _currentNode.Next;
+			}
+
+			_host.UndoRedoState = _currentNode?.Value;
         }
 
         public void Snapshot()