From e0a8248fba84bd21920dc45c91c9f18e1fd99128 Mon Sep 17 00:00:00 2001
From: Max Katz <maxkatz6@outlook.com>
Date: Thu, 14 Jan 2021 21:31:17 -0500
Subject: [PATCH 1/2] Close tooltip on null Tip value

---
 src/Avalonia.Controls/ToolTipService.cs | 13 ++++++++++---
 1 file changed, 10 insertions(+), 3 deletions(-)

diff --git a/src/Avalonia.Controls/ToolTipService.cs b/src/Avalonia.Controls/ToolTipService.cs
index 9e0bf60f42..f6458c2112 100644
--- a/src/Avalonia.Controls/ToolTipService.cs
+++ b/src/Avalonia.Controls/ToolTipService.cs
@@ -38,9 +38,16 @@ namespace Avalonia.Controls
 
             if (ToolTip.GetIsOpen(control) && e.NewValue != e.OldValue && !(e.NewValue is ToolTip))
             {
-                var tip = control.GetValue(ToolTip.ToolTipProperty);
-
-                tip.Content = e.NewValue;
+                if (e.NewValue is null)
+                {
+                    Close(control);
+                }
+                else
+                {
+                    var tip = control.GetValue(ToolTip.ToolTipProperty);
+
+                    tip.Content = e.NewValue;
+                }
             }
         }
 

From dc7e33e4f3ea1e498b484eea93ee0fddcc83e690 Mon Sep 17 00:00:00 2001
From: Max Katz <maxkatz6@outlook.com>
Date: Thu, 14 Jan 2021 21:45:23 -0500
Subject: [PATCH 2/2] Add Should_Close_On_Null_Tip test

---
 .../ToolTipTests.cs                           | 28 +++++++++++++++++++
 1 file changed, 28 insertions(+)

diff --git a/tests/Avalonia.Controls.UnitTests/ToolTipTests.cs b/tests/Avalonia.Controls.UnitTests/ToolTipTests.cs
index 9279e78013..25969a58e3 100644
--- a/tests/Avalonia.Controls.UnitTests/ToolTipTests.cs
+++ b/tests/Avalonia.Controls.UnitTests/ToolTipTests.cs
@@ -270,6 +270,34 @@ namespace Avalonia.Controls.UnitTests
                 Assert.Empty(toolTip.Classes);
             }
         }
+
+        [Fact]
+        public void Should_Close_On_Null_Tip()
+        {
+            using (UnitTestApplication.Start(TestServices.StyledWindow))
+            {
+                var window = new Window();
+
+                var target = new Decorator()
+                {
+                    [ToolTip.TipProperty] = "Tip",
+                    [ToolTip.ShowDelayProperty] = 0
+                };
+
+                window.Content = target;
+
+                window.ApplyTemplate();
+                window.Presenter.ApplyTemplate();
+
+                _mouseHelper.Enter(target);
+
+                Assert.True(ToolTip.GetIsOpen(target));
+
+                target[ToolTip.TipProperty] = null;
+
+                Assert.False(ToolTip.GetIsOpen(target));
+            }
+        }
     }
 
     internal class ToolTipViewModel