WPF GridSplitter after resize

Once the gridsplitter is used to resize a grid the row * will not reclaim the space when the other rows are collapsed.

I have the following grid in a master detail view with three rows. A data grid on top a splitter in the middle and a contentcontrol view in the last row. The splitter has a close button on it to collapse the detail. This all works with the exception that once the user resizes using the gridsplitter.

    <Grid Margin="3,0">
    <Grid.RowDefinitions>
        <RowDefinition Height="*"/>
        <RowDefinition Style="{StaticResource CollapsableRow}"/><!-- Splitter Here -->
        <RowDefinition Style="{StaticResource CollapsableRow}"/>
    </Grid.RowDefinitions>

The GridSplitter style:

    <Style x:Key="gridSplitterStyle" TargetType="{x:Type GridSplitter}">
    <Setter Property="Visibility" Value="{Binding IsItemSelected, Converter={StaticResource BoolToShow},ConverterParameter='Visible|Collapsed'}" />
    <Setter Property="Width" Value="Auto"/>
    <Setter Property="Height" Value="14"/>
    <Setter Property="HorizontalAlignment" Value="Stretch"/>
    <Setter Property="Border.BorderBrush" Value="#FF6593CF" />
    <Setter Property="Border.BorderThickness" Value="0,1,0,0" />
    <Setter Property="UIElement.SnapsToDevicePixels" Value="True" />
    <Setter Property="UIElement.Focusable" Value="False" />
    <Setter Property="Control.Padding" Value="7,7,7,7" />
    <Setter Property="Cursor" Value="SizeNS" /></Style>

Like I said the collapse works correctly unless the gridsplitter is used to resize. After that the whitespace stays.

EDIT: H.B. and codenaked had simple and consistant suggestions so and I attempted to implement them w/o success in a data trigger:

<Style x:Key="CollapsableRow" TargetType="{x:Type RowDefinition}">
    <Style.Triggers>
        <DataTrigger Binding="{Binding SelectedItem, Converter={StaticResource IsNullConverter}}" Value="True">
            <Setter Property="RowDefinition.Height" Value="0"/>
        </DataTrigger>
        <DataTrigger Binding="{Binding SelectedItem, Converter={StaticResource IsNullConverter}}" Value="False">
            <Setter Property="RowDefinition.Height" Value="Auto"/>
        </DataTrigger>            
    </Style.Triggers>
</Style>