<Window x:Class="TestOfNull.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
Title="x:Null Sample" Height="350" Width="525">
<Window.Resources>
<Style x:Key="{x:Type Button}" TargetType="{x:Type Button}" >
<Setter Property="Width" Value="60" />
<Setter Property="Height" Value="36" />
<Setter Property="Margin" Value="5" />
</Style>
</Window.Resources>
<StackPanel >
<Button Content="OK" />
<Button Content="OK" />
<Button Content="OK" />
<Button Content="OK" Style="{x:Null}" />
</StackPanel>
</Window>