XAML触发器作为静态资源

<Window.Resources>
    <Trigger x:Key="ValidationTrigger" x:Shared="False" Property="Validation.HasError" Value="true">
        <Setter Property="FrameworkElement.ToolTip"
                Value="{Binding RelativeSource={x:Static RelativeSource.Self},
                Path=(Validation.Errors)/ErrorContent}"/>
    </Trigger>

    <Style TargetType="{x:Type TextBox}" BasedOn="{StaticResource {x:Type TextBox}}">
        <Style.Triggers>
            <StaticResource ResourceKey="ValidationTrigger"/>
        </Style.Triggers>
    </Style>
</Window.Resources>

我在运行时收到一条错误消息
“值不能为空。