Conditional formatting for the Header content - wpf

Question

I have the following template for some header:
<telerik:RadExpander.Header>
<StackPanel Orientation="Horizontal" DataContext="{Binding CurrentItem, ElementName=activityProductGrid}">
<TextBlock Text="{Binding Strings[Product], Source={StaticResource LanguageResources}, StringFormat='{}{0}: '}" />
<TextBlock Text="{Binding Product.Name}" FontWeight="Bold" />
<TextBlock Text="{Binding Strings[GroupName], Source={StaticResource LanguageResources}, StringFormat=', {0}: '}" />
<TextBlock Text="{Binding GroupName}" />
<TextBlock Text="{Binding Strings[UnitPrice], Source={StaticResource LanguageResources}, StringFormat=', {0}: '}" />
<TextBlock Text="{Binding UnitPrice}" />
</StackPanel>
</telerik:RadExpander.Header>
How can I do conditional formmatting of the header, if for example Product == null, then Header should not display anything?
Edit: This one works.
<StackPanel Orientation="Horizontal" DataContext="{Binding CurrentItem, ElementName=activityProductGrid}">
<i:Interaction.Triggers>
<ie:DataTrigger Binding="{Binding}" Value="{x:Null}">
<ie:ChangePropertyAction TargetObject="{RelativeSource={RelativeSource AncestorType=StackPanel}}" PropertyName="Visibility">
<ie:ChangePropertyAction.Value>
<Visibility>Collapsed</Visibility>
</ie:ChangePropertyAction.Value>
</ie:ChangePropertyAction>
</ie:DataTrigger>
</i:Interaction.Triggers>
<-- from this point the came code as above -->
</StackPanel>

Answer 1

Specifically for null, you can specify binding parameters for a replacement value, or one to display in case of binding errors:
<TextBlock
Text="{Binding Product.Name, TargetNullValue=(empty), FallbackValue=(error)}"/>
(Taken from the WPF Binding Cheatsheet)
EDIT: I noticed that you didn't just want a specific binding to have a different value, but the whole control to not be displayed. For this, you can use Styles and Triggers, binging a DataTrigger to your Product property, and setting Visibility if it's null.
<telerik:RadExpander.Header>
<StackPanel>
<StackPanel.Style>
<Style TargetType="StackPanel">
<Style.Triggers>
<DataTrigger Binding="{Binding Product}" Value="{x:Null}">
<Setter Property="Visibility" Value="Collapsed"/>
</DataTrigger>
</Style.Triggers>
</Style>
</StackPanel.Style>
</StackPanel>
</telerik:RadExpander.Header>