Hi i am trying to generate visio drwaings using powershell but getting the following error;

PS C:\Users\XXXX\Desktop\Scripts> C:\Users\XXXX\Desktop\Scripts\tempv.ps1

You cannot call a method on a null-valued expression.

At C:\Users\XXXX\Desktop\Scripts\tempv.ps1:14 char:1

+ $pc = $ComputerStencil.Masters.Page("PC")

+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

+ CategoryInfo : InvalidOperation: (:) [], RuntimeException

+ FullyQualifiedErrorId : InvokeMethodOnNull

PS C:\Users\XXXX\Desktop\Scripts>

Please tell me whats wrong here ; i tried lot but couldnt get whats wrong;

$application = New-Object -ComObject Visio.Application
#$application.visible = $false
$documents = $application.Documents
$document = $documents.Add("Basic Network Diagram.vst")
$pages = $application.ActiveDocument.Pages
$page = $pages.Item(1)
$NetworkStencil = $documents.Add("periph_m.vss")
$ComputerStencil = $documents.Add("Computers and Monitors.vss")
$ConnectorStencil = $documents.Add("Connectors.vss")
$pcinfo = Get-ComputerSystem -computer $computer
#***********************WORKS UNTILL HERE**************
#*****ERROR PART***************
$pc = $ComputerStencil.Masters.Page("PC")
$shape1 = $page.Drop($pc, 2.2, 6.8)
$shape1.Text = "$($pcinfo.DNSHostName)`r`n$($pcinfo.Domain)"