MultiDataTrigger conditions null check - wpf

Question

I am trying to setup a grid's visibility using a multidatatrigger. The condition for making it visible is PropertyA==null && PropertyB==false. I am not sure how PropertyA condition is to be written. My attempt is here (but not working):
<Grid>
<Grid.Style>
<Style>
<Setter Property="Control.Visibility" Value="Collapsed"/>
<Style.Triggers>
<MultiDataTrigger>
<MultiDataTrigger.Conditions>
<Condition Binding="{Binding PropertyA}" Value="{x:Null}"/>
<Condition Binding="{Binding PropertyB}" Value="False"/>
</MultiDataTrigger.Conditions>
<Setter Property="Control.Visibility" Value="Visible" />
</MultiDataTrigger>
</Style.Triggers>
</Style>
</Grid.Style>
Could someone advise pls.

Answer 1

This is the style that I have used, it is for Button but it works as expected
<Style TargetType="Button" x:Key="btnTakePhoto">
<Style.Triggers>
<MultiDataTrigger>
<MultiDataTrigger.Conditions>
<Condition Binding="{Binding Comment}" Value="{x:Null}"/>
<Condition Binding="{Binding ResponseNumber}" Value="{x:Null}"/>
</MultiDataTrigger.Conditions>
<Setter Property="Visibility" Value="Collapsed"/>
</MultiDataTrigger>
</Style.Triggers>
</Style>
Try to take the Style out of your Grid and include it in your UserControl.Resources tag.
You would use it like so:
<Button Style="{StaticResource btnTakePhoto}"/>
There is absolutely no reason for your xaml not to work.
EDIT
Also I have this code in my other UserControl:
<Grid>
<Grid.RowDefinitions>
<RowDefinition/>
<RowDefinition Height="Auto"/>
</Grid.RowDefinitions>
<Grid.Style>
<Style>
<Setter Property="Grid.Visibility" Value="Collapsed"/>
<Style.Triggers>
<DataTrigger Binding="{Binding ElementName=btnShowHide, Path=IsChecked}" Value="True">
<Setter Property="Grid.Visibility" Value="Visible"/>
</DataTrigger>
</Style.Triggers>
</Style>
</Grid.Style>
</Grid>
<ToggleButton MinHeight="150" Width="50" Content=">" Name="btnShowHide">