title: WPF Datatrigger Visibility + Null Value
body: <p>I'm beginner in WPF.
  I want to set Visibility to Hidden on a Radiobutton when the databind value is equal to Null.
  I'm using WPF Toolkit.
  This is my code but it doesn't work :</p>
  
  <pre><code>    &lt;dg:DataGrid x:Name="dtGrdData" HorizontalScrollBarVisibility="Hidden" SelectionMode="Extended" CanUserAddRows="False" CanUserDeleteRows="False" CanUserResizeRows="False" CanUserSortColumns="False" AutoGenerateColumns="False"
                   RowHeaderWidth="0" RowHeight="50" &gt;
          &lt;DataTrigger Binding="{Binding P_DAY_PRICE}" Value="{x:Null}"&gt;
              &lt;Setter Property="RadioButton.Visibility" Value="Hidden"&gt;&lt;/Setter&gt;
          &lt;/DataTrigger&gt;
          &lt;dg:DataGrid.Columns&gt;
              &lt;dg:DataGridTemplateColumn Header="1 day" Width="1.5*" &gt;
                  &lt;dg:DataGridTemplateColumn.CellTemplate&gt;
                      &lt;DataTemplate&gt;
                          &lt;RadioButton x:Name="rdBtnDayPrice" GroupName="grpNmPrice" Content="{Binding Path=P_DAY_PRICE}" Style="{StaticResource toggleStyle}" Checked="RadioButton_Checked"&gt;&lt;/RadioButton&gt;
                      &lt;/DataTemplate&gt;
                  &lt;/dg:DataGridTemplateColumn.CellTemplate&gt;
              &lt;/dg:DataGridTemplateColumn&gt;
          &lt;/dg:DataGrid.Columns&gt;
      &lt;/dg:DataGrid&gt;
  </code></pre>
  
  <p>Can you help me ?
  Thanks</p>