Data-Trigger Binding not working as expected

Question

I have an style which defines a template for content controls.

For all controls that have the content property null, I'd like to show text saying the control is empty... but the xaml below is not working, does anybody know why?

        <Style TargetType="ContentControl" x:Key="style">
            <Style.Triggers>
                <DataTrigger Binding="{Binding Path=Content, RelativeSource={RelativeSource Self}}" Value="{x:Null}">
                    <Setter Property="ContentControl.Template">
                        <Setter.Value>
                            <ControlTemplate>
                                <Grid HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
                                    <TextBlock Background="Blue">EMPTY!</TextBlock>
                                </Grid>
                            </ControlTemplate>
                        </Setter.Value>
                    </Setter>
                </DataTrigger>
            </Style.Triggers>
        </Style>

<ContentControl Content="{x:Null}" Style="{StaticResource style}" />

It's not showing me the text 'EMPTY!'.

Answer 1

The following works:

<Window x:Class="WpfApplication1.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">    
    <Window.Resources>
    <Style TargetType="ContentControl" x:Key="style">
        <Style.Triggers>
            <DataTrigger Binding="{Binding Path=Content, RelativeSource={RelativeSource Self}}" Value="{x:Null}">
                <Setter Property="ContentControl.Template">
                    <Setter.Value>
                        <ControlTemplate>
                            <Grid HorizontalAlignment="Stretch" VerticalAlignment="Stretch">
                                <TextBlock Background="Blue">EMPTY!</TextBlock>
                            </Grid>
                        </ControlTemplate>
                    </Setter.Value>
                </Setter>
            </DataTrigger>
        </Style.Triggers>
    </Style>     
    </Window.Resources>
    <Grid>
        <ContentControl Content="{x:Null}" Style="{StaticResource style}" />
    </Grid>
</Window>