How to hide the empty TextBlock?

In the XAML provided below, I don't have the value for Phone sometimes. When that happens, the value is missing, but the TextBlock is still occupying the space in the panel. I want to hide empty TextBlocks from taking space in the StackPanel.

Here's the XAML:

<StackPanel>
    <TextBlock Text="{Binding Path=FirstName}" />
    <TextBlock Text="{Binding Path=LastName}" />
    <TextBlock Text="{Binding Path=Phone}" />
    <TextBlock Text="{Binding Path=Email}" />
</StackPanel>

I've read this article, but the accepted answer doesn't work for me:

<StackPanel>
    <TextBlock Text="{Binding Path=FirstName}" />
    <TextBlock Text="{Binding Path=LastName}" />
    <TextBlock Text="{Binding Path=Phone}">
        <TextBlock.Style>
            <Style TargetType="TextBlock">
                <Style.Triggers>
                    <Trigger Property="Text" Value="{x:Null}">
                        <Setter Property="Visibility" Value="Collapsed" />
                    </Trigger>
                </Style.Triggers>
            </Style>
        </TextBlock.Style>
    </TextBlock>
    <TextBlock Text="{Binding Path=Email}" />
</StackPanel>

Am I making a mistake somewhere, or is the accepted answer wrong? What should I do to achieve my goal?