diff --git a/src/Avalonia.Base/Data/Converters/ObjectConverters.cs b/src/Avalonia.Base/Data/Converters/ObjectConverters.cs
new file mode 100644
index 0000000000..3cadfd5b47
--- /dev/null
+++ b/src/Avalonia.Base/Data/Converters/ObjectConverters.cs
@@ -0,0 +1,24 @@
+// Copyright (c) The Avalonia Project. All rights reserved.
+// Licensed under the MIT license. See licence.md file in the project root for full license information.
+
+
+namespace Avalonia.Data.Converters
+{
+    /// <summary>
+    /// Provides a set of useful <see cref="IValueConverter"/>s for working with objects.
+    /// </summary>
+    public static class ObjectConverters
+    {
+        /// <summary>
+        /// A value converter that returns true if the input object is a null reference.
+        /// </summary>
+        public static readonly IValueConverter IsNull =
+            new FuncValueConverter<object, bool>(x => x is null);
+
+        /// <summary>
+        /// A value converter that returns true if the input object is not null.
+        /// </summary>
+        public static readonly IValueConverter IsNotNull =
+            new FuncValueConverter<object, bool>(x => !(x is null));
+    }
+}
diff --git a/src/Avalonia.Base/Data/Converters/StringConverters.cs b/src/Avalonia.Base/Data/Converters/StringConverters.cs
index 0101cf5d29..42eb8e1d81 100644
--- a/src/Avalonia.Base/Data/Converters/StringConverters.cs
+++ b/src/Avalonia.Base/Data/Converters/StringConverters.cs
@@ -12,13 +12,13 @@ namespace Avalonia.Data.Converters
         /// <summary>
         /// A value converter that returns true if the input string is null or an empty string.
         /// </summary>
-        public static readonly IValueConverter NullOrEmpty =
+        public static readonly IValueConverter IsNullOrEmpty =
             new FuncValueConverter<string, bool>(string.IsNullOrEmpty);
 
         /// <summary>
         /// A value converter that returns true if the input string is not null or empty.
         /// </summary>
-        public static readonly IValueConverter NotNullOrEmpty =
+        public static readonly IValueConverter IsNotNullOrEmpty =
             new FuncValueConverter<string, bool>(x => !string.IsNullOrEmpty(x));
     }
 }
diff --git a/src/Avalonia.Controls/ContentControl.cs b/src/Avalonia.Controls/ContentControl.cs
index 20ec581108..6da6da54a5 100644
--- a/src/Avalonia.Controls/ContentControl.cs
+++ b/src/Avalonia.Controls/ContentControl.cs
@@ -45,8 +45,6 @@ namespace Avalonia.Controls
         static ContentControl()
         {
             ContentControlMixin.Attach<ContentControl>(ContentProperty, x => x.LogicalChildren);
-            PseudoClass<ContentControl, object>(ContentProperty, x => x != null, ":valid");
-            PseudoClass<ContentControl, object>(ContentProperty, x => x == null, ":invalid");
         }
 
         /// <summary>
diff --git a/src/Avalonia.Controls/NumericUpDown/NumericUpDown.cs b/src/Avalonia.Controls/NumericUpDown/NumericUpDown.cs
index 1f8e991d2e..18cef7d64e 100644
--- a/src/Avalonia.Controls/NumericUpDown/NumericUpDown.cs
+++ b/src/Avalonia.Controls/NumericUpDown/NumericUpDown.cs
@@ -287,6 +287,13 @@ namespace Avalonia.Controls
             ValueProperty.Changed.Subscribe(OnValueChanged);
         }
 
+        /// <inheritdoc />
+        protected override void OnLostFocus(RoutedEventArgs e)
+        {
+            CommitInput();
+            base.OnLostFocus(e);
+        }
+
         /// <inheritdoc />
         protected override void OnTemplateApplied(TemplateAppliedEventArgs e)
         {
diff --git a/src/Avalonia.Themes.Default/CheckBox.xaml b/src/Avalonia.Themes.Default/CheckBox.xaml
index e2301b9b09..f87ae2674f 100644
--- a/src/Avalonia.Themes.Default/CheckBox.xaml
+++ b/src/Avalonia.Themes.Default/CheckBox.xaml
@@ -1,9 +1,10 @@
-<Styles xmlns="https://github.com/avaloniaui">
+<Styles xmlns="https://github.com/avaloniaui" xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml">
   <Style Selector="CheckBox">
     <Setter Property="Foreground" Value="{DynamicResource ThemeForegroundBrush}"/>
     <Setter Property="Background" Value="Transparent"/>
     <Setter Property="BorderBrush" Value="{DynamicResource ThemeBorderMidBrush}"/>
     <Setter Property="BorderThickness" Value="{DynamicResource ThemeBorderThickness}"/>
+    <Setter Property="Padding" Value="4,0,0,0"/>
     <Setter Property="VerticalContentAlignment" Value="Center"/>
     <Setter Property="HorizontalContentAlignment" Value="Left"/>
     <Setter Property="Template">
@@ -38,17 +39,15 @@
                             TextBlock.Foreground="{TemplateBinding Foreground}"
                             ContentTemplate="{TemplateBinding ContentTemplate}"
                             Content="{TemplateBinding Content}"
-                            Margin="4,0,0,0"
+                            Margin="{TemplateBinding Padding}"
                             VerticalAlignment="{TemplateBinding VerticalContentAlignment}"
                             HorizontalAlignment="{TemplateBinding HorizontalContentAlignment}"
+                            IsVisible="{TemplateBinding Content, Converter={x:Static ObjectConverters.IsNotNull}}"
                             Grid.Column="1"/>
         </Grid>
       </ControlTemplate>
     </Setter>
   </Style>
-  <Style Selector="CheckBox:invalid /template/ ContentPresenter#PART_ContentPresenter">
-    <Setter Property="IsVisible" Value="False"/>
-  </Style>
   <Style Selector="CheckBox:pointerover /template/ Border#border">
     <Setter Property="BorderBrush" Value="{DynamicResource ThemeBorderHighBrush}"/>
   </Style>
diff --git a/src/Avalonia.Themes.Default/TextBox.xaml b/src/Avalonia.Themes.Default/TextBox.xaml
index 90100c2f2b..6741bdc7d9 100644
--- a/src/Avalonia.Themes.Default/TextBox.xaml
+++ b/src/Avalonia.Themes.Default/TextBox.xaml
@@ -23,7 +23,7 @@
                            Path="UseFloatingWatermark"/>
                   <Binding RelativeSource="{RelativeSource TemplatedParent}"
                            Path="Text"
-                           Converter="{x:Static StringConverters.NotNullOrEmpty}"/>
+                           Converter="{x:Static StringConverters.IsNotNullOrEmpty}"/>
                 </MultiBinding>
               </TextBlock.IsVisible>
             </TextBlock>
@@ -36,7 +36,7 @@
                   <TextBlock Name="watermark"
                              Opacity="0.5"
                              Text="{TemplateBinding Watermark}"
-                             IsVisible="{TemplateBinding Text, Converter={x:Static StringConverters.NullOrEmpty}}"/>
+                             IsVisible="{TemplateBinding Text, Converter={x:Static StringConverters.IsNullOrEmpty}}"/>
                   <TextPresenter Name="PART_TextPresenter"
                                  Text="{TemplateBinding Text, Mode=TwoWay}"
                                  CaretIndex="{TemplateBinding CaretIndex}"
diff --git a/tests/Avalonia.Markup.UnitTests/Data/BindingTests_Converters.cs b/tests/Avalonia.Markup.UnitTests/Data/BindingTests_Converters.cs
index 123aadfda5..1ede4ee0b0 100644
--- a/tests/Avalonia.Markup.UnitTests/Data/BindingTests_Converters.cs
+++ b/tests/Avalonia.Markup.UnitTests/Data/BindingTests_Converters.cs
@@ -22,14 +22,14 @@ namespace Avalonia.Markup.UnitTests.Data
 
             var target = new Binding(nameof(Class1.Foo))
             {
-                Converter = StringConverters.NullOrEmpty,
+                Converter = StringConverters.IsNullOrEmpty,
             };
 
             var expressionObserver = (BindingExpression)target.Initiate(
                 textBlock, 
                 TextBlock.TextProperty).Observable;
 
-            Assert.Same(StringConverters.NullOrEmpty, expressionObserver.Converter);
+            Assert.Same(StringConverters.IsNullOrEmpty, expressionObserver.Converter);
         }
 
         public class When_Binding_To_String
@@ -129,7 +129,7 @@ namespace Avalonia.Markup.UnitTests.Data
 
             var target = new Binding(nameof(Class1.Foo))
             {
-                Converter = StringConverters.NotNullOrEmpty,
+                Converter = StringConverters.IsNotNullOrEmpty,
                 StringFormat = "Hello {0}",
             };