I tried to create a Volto app within my cloned Github repository github.com/plone/volto following the instructions in the readme file.
I installed yarn and @plone/create-volto-app using npm.
The command create-volto-app myvoltoapp failed with:
Success! Created files for "myvoltoapp" Volto app
Installing npm modules: @plone/volto
Error! Failed to install @plone/volto, try again.
Can you please create an issue on github for this on the create-volto-app repo? You have the latest Node 12 and I never saw a trace with just "undefined". Maybe we can enhance create-volto-app with a "-v" param that outputs more info. Please include what kind of OS you are using and how you installed node.