Null-valued expression error in Powershell script with GUI Runspace - wpf

Question

I have a configuration script in powershell that I am trying to marry with a WFP GUI. After a few failed forays with code and gui in the same thread I have been reading a number of pages about running the GUI in its own runspace. Below is the code that I have pieced together.
The form runs but I get this error related to the button click I am trying to use to hide/unhide grids.
You cannot call a method on a null-valued expression.
At C:\Projects\AVPC Setup\Working Files\MT Trial 3.ps1:218 char:18
+ $syncHash.fullConfig.Add_Click({
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+ CategoryInfo : InvalidOperation: (:) [], RuntimeException
+ FullyQualifiedErrorId : InvokeMethodOnNull
With the form running these variables are visible in the syncHash so I am not sure what I am missing.
$Global:syncHash = [hashtable]::Synchronized(#{})
$newRunspace =[runspacefactory]::CreateRunspace()
$newRunspace.ApartmentState = "STA"
$newRunspace.Name = "Config GUI"
$newRunspace.ThreadOptions = "ReuseThread"
$newRunspace.Open()
$newRunspace.SessionStateProxy.SetVariable("syncHash",$syncHash)
$psCmd = [PowerShell]::Create().AddScript({
[xml]$xaml = #"
<Window x:Class="psguiconfig.MainWindow"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
xmlns:d="http://schemas.microsoft.com/expression/blend/2008"
xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"
xmlns:local="clr-namespace:psguiconfig"
mc:Ignorable="d"
Title="Config" Height="175" Width="500">
<Grid x:Name="mainGrid" HorizontalAlignment="Left" Height="144" Margin="0,1,0,0" VerticalAlignment="Top" Width="490">
<Grid x:Name="choiceGrid" HorizontalAlignment="Left" Height="144" Margin="0,1,0,0" VerticalAlignment="Top" Width="490" Visibility="Visible">
<Label Content="Choose Config Type" HorizontalAlignment="Center" Height="26" Margin="0,0,0,60" VerticalAlignment="Center" FontWeight="SemiBold"/>
<Button x:Name="fullConfig" Content="Full" HorizontalAlignment="Center" Margin="0,45,250,0" VerticalAlignment="Center" Width="75"/>
<Button x:Name="stepConfig" Content="Step By Step" HorizontalAlignment="Center" Margin="0,45,0,0" VerticalAlignment="Center" Width="75"/>
<Button x:Name="upgradeConfig" Content="Upgrade" HorizontalAlignment="Center" Margin="250,45,0,0" VerticalAlignment="Center" Width="75" IsEnabled="False"/>
</Grid>
<Grid x:Name="fullGrid" HorizontalAlignment="Left" Height="144" Margin="0,1,0,0" VerticalAlignment="Top" Width="490" Visibility="Hidden">
<Label x:Name="fullLabel" Content="Full Config" HorizontalAlignment="Center" Height="26" Margin="0,0,0,60" VerticalAlignment="Center" FontWeight="SemiBold"/>
<ProgressBar x:Name="fullProgress" HorizontalAlignment="Center" Height="20" Margin="0,40,0,0" VerticalAlignment="Center" Width="400"/>
<Label x:Name="fullProgressLabel" Content="Tasking Stuffs" Foreground="#FFFFFF" HorizontalAlignment="Center" Height="20" Margin="45,82,245,42" VerticalAlignment="Center" FontWeight="SemiBold" FontSize="7" Width="200"/>
<Label x:Name="fullProgressPercentageLabel" Content="0%" Foreground="#FFFFFF" HorizontalContentAlignment="Right" Height="20" Margin="419,82,45,42" VerticalAlignment="Center" FontWeight="SemiBold" FontSize="7" Width="26"/>
</Grid>
</Grid>
</Window>
"#
$AttributesToRemove = #(
'x:Class',
'mc:Ignorable'
)
foreach ($Attrib in $AttributesToRemove) {
if ( $xaml.Window.GetAttribute($Attrib) ) {
$xaml.Window.RemoveAttribute($Attrib)
}
}
$reader=(New-Object System.Xml.XmlNodeReader $xaml)
$syncHash.Window=[Windows.Markup.XamlReader]::Load( $reader )
[xml]$XAML = $xaml
$xaml.SelectNodes("//*[#*[contains(translate(name(.),'n','N'),'Name')]]") | %{
#Find all of the form types and add them as members to the synchash
$syncHash.Add($_.Name,$syncHash.Window.FindName($_.Name) )
}
$syncHash.Window.ShowDialog() | Out-Null
$syncHash.Error = $Error
})
$psCmd.Runspace = $newRunspace
$data = $psCmd.BeginInvoke()
Function Update-Window {
Param (
$Control,
$Property,
$Value,
[switch]$AppendContent
)
If ($Property -eq "Close") {
$syncHash.Window.Dispatcher.invoke([action]{$syncHash.Window.Close()},"Normal")
Return
}
$syncHash.$Control.Dispatcher.Invoke([action]{
If ($PSBoundParameters['AppendContent']) { $syncHash.$Control.AppendText($Value) } Else { $syncHash.$Control.$Property = $Value }
}, "Normal")
}
$syncHash.fullConfig.Add_Click({
Update-Window -Control choiceGrid -Property Visibility -Value Hidden
Update-Window -Control fullGrid -Property Visibility -Value Visible
})