Define <Null> Value for UniqueValueMultipleFieldsInfo

[Todd]

Been a while, hello friends. Trying to set a renderer based on a value of <Null> for the Values property of UniqueValueMultipleFieldsInfo. The 3 below work fine, however I'm looking to render a value for Values="null,null" which is present in the database.

Here is the stub:

<esri:UniqueValueMultipleFieldsRenderer  x:Key="PermitsUniqueValueRenderer" Fields="MPCK_HASPOOL,HASPOOL_ORIG" >
                <esri:UniqueValueMultipleFieldsRenderer.Infos >
                    <esri:UniqueValueMultipleFieldsInfo Values="Y,A" Symbol="{StaticResource YesPool}" Label="Pool"/>
                    <esri:UniqueValueMultipleFieldsInfo Values="N,A" Symbol="{StaticResource NoPool}" Label="No Pool"/>
                    <esri:UniqueValueMultipleFieldsInfo Values="A,A" Symbol="{StaticResource OBYYesPool}" Label="OBY: Pool"/>                  
                </esri:UniqueValueMultipleFieldsRenderer.Infos>                
            </esri:UniqueValueMultipleFieldsRenderer>

This won't work but gives a visual of what I'm after:

<esri:UniqueValueMultipleFieldsInfo Values="null,null" Symbol="{StaticResource OBYNoPool}" Label="OBY: No Pool"/>

Not a whole lot of documentation on this, so thanks in advance!