Apply-PnPTenantTemplate : Object reference not set to an instance of an object

Hello, Object reference not set to an instance of an object, my old friend. Good to see you again.

Recently attempting to apply a PnP Tenant Template to an environment and ran into the above non-descript error message:

Apply-PnPTenantTemplate -Path C:\temp\client\provisioning\client.xml -Parameters @{"SiteURL"="https://clienttenant.sharepoint.com/sites/targetsite"} -Verbose

Apply-PnPTenantTemplate : Object reference not set to an instance of an object.
At line:1 char:1
+ Apply-PnPTenantTemplate -Path C:\temp\client\provisioning\client.xml -Para ...
+ ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
    + CategoryInfo          : WriteError: (:) [Apply-PnPTenantTemplate], NullReferenceException
    + FullyQualifiedErrorId : EXCEPTION,SharePointPnP.PowerShell.Commands.Provisioning.Tenant.ApplyTenantTemplate

I reached out the the dev team and asked for some support - it's great to have a solid dev team - and they asked me to confirm that I'm running the latest version of the SharePointPnPPowerShellOnline module. They were nice enough to provide a PowerShell one-liner to do just this:

Get-Module SharePointPnPPowerShell* -ListAvailable | Select-Object Name,Version | Sort-Object Version -Descending

Now this isn't my first rodeo, so I updated the module specifying the -AllowClobber and -Force parameters. Following that I re-ran the Apply-PnPTenantTemplate cmdlet - it failed again.

Time to figure out exactly what version of SharePointPnPPowerShellOnline I had installed:

Name                          Version
----                          -------
SharePointPnPPowerShellOnline 3.9.1905.3
SharePointPnPPowerShell2016   3.9.1905.3
SharePointPnPPowerShellOnline 3.0.1808.1
SharePointPnPPowerShellOnline 2.27.1806.1
SharePointPnPPowerShell2016   2.27.1806.0
SharePointPnPPowerShell2016   2.25.1804.1

Not only did I have the latest installed, but I'd managed to side-by-side install it with prior versions - that's the -AllowClobber and -Force at work. The result of this seems to create a scenario where certain commands are executed by prior versions of the same module, and this case that made for a failed deployment.

The fix was to run Uninstall-Module for the offending versions and then retry the Apply-PnPTenantTemplate. For the future, I'm going to look at Using SharePoint PnP PowerShell Modules Side-by-Side as Chris Kent details on his blog.