Creating of package fails if Version attribute is left out from package.xml

According to the DevGuide the Version attribute is optional: https://gitlab.com/OpenTAP/opentap/blob/master/doc/Developer%20Guide/Plugin%20Packaging%20and%20Versioning/Readme.md#packaging-configuration-file

If I leave Version out of package.xml:

<Package Name="OpenTap.Plugins.MyPlugin" OS="Windows,Linux" Architecture="AnyCPU" xmlns="http://opentap.io/schemas/package">

I get this error during package creation:

00:00:01.244 : PackageAction : Error       : Object reference not set to an instance of an object.
00:00:01.246 : PackageAction : Debug       : Exception: Object reference not set to an instance of an object.
00:00:01.254 : PackageAction : Debug       :     at OpenTap.Package.PackageCreateAction.Process(String[] OutputPaths)

This does not happen if I include an empty Version:

<Package Name="OpenTap.Plugins.MyPlugin4" Version="" OS="Windows,Linux" Architecture="AnyCPU" xmlns="http://opentap.io/schemas/package">