Error: Could not install … Error: Value cannot be null. Parameter name: key Usage: new [options] …
When building a new solution template for ASP.NET Core solution, I received the above error.  I had not seen this with prior template build efforts.  This was new with .NET Core.
The error occurs when one of the node_modules folders contain a template.json file.  The solution for me, was to entirely remove the node_modules directory before attempting to build the template.
Reference: https://github.com/dotnet/cli/issues/8989