From e80e52c3036fc76b3e2cd8d5be37096e2198d951 Mon Sep 17 00:00:00 2001
From: Steven Kirk <grokys@gmail.com>
Date: Mon, 17 Feb 2020 15:27:35 +0100
Subject: [PATCH] TryGetValue doesn't allow null as the value.

---
 .../Generators/TreeContainerIndex.cs          | 20 +++++++++++++------
 1 file changed, 14 insertions(+), 6 deletions(-)

diff --git a/src/Avalonia.Controls/Generators/TreeContainerIndex.cs b/src/Avalonia.Controls/Generators/TreeContainerIndex.cs
index 0da84008f6..ca417e0d45 100644
--- a/src/Avalonia.Controls/Generators/TreeContainerIndex.cs
+++ b/src/Avalonia.Controls/Generators/TreeContainerIndex.cs
@@ -97,9 +97,13 @@ namespace Avalonia.Controls.Generators
         /// <returns>The container, or null of not found.</returns>
         public IControl ContainerFromItem(object item)
         {
-            IControl result;
-            _itemToContainer.TryGetValue(item, out result);
-            return result;
+            if (item != null)
+            {
+                _itemToContainer.TryGetValue(item, out var result);
+                return result;
+            }
+
+            return null;
         }
 
         /// <summary>
@@ -109,9 +113,13 @@ namespace Avalonia.Controls.Generators
         /// <returns>The item, or null of not found.</returns>
         public object ItemFromContainer(IControl container)
         {
-            object result;
-            _containerToItem.TryGetValue(container, out result);
-            return result;
+            if (container != null)
+            {
+                _containerToItem.TryGetValue(container, out var result);
+                return result;
+            }
+
+            return null;
         }
     }
 }