I was building a PowerShell cmdlet aimed at SharePoint 2013 earlier tonight and after deploying my WSP I was getting the following cryptic error.
Cannot process argument because the value of argument "implementingType" is null. Change the value of argument "implementingType" to a non-null value.
The error claimed to be a result of attempting to load the help XML file although this turned out to be a bit of a red-herring in my case.
Searching around online didn’t really show much so I thought I’d leave a quick note here about what eventually solved it for me. It turned out that in my registration XML (found under hive/CONFIG/POWERSHELL/Registration) I had declared the wrong assembly. By default my registration XML was using a $SharePoint.Project.AssemblyFullName$ token which would be fine in certain circumstances but as my assembly was being built in a different project with a different key, this was being filled in with the wrong details. After changing the <ps:Assembly Name=”$SharePoint.Project.AssemblyFullName$”> tag to declare the correct assembly, I stopped getting the above error.