Trying to create a proxy for npm.pkg.github.com, but Nexus does not work because it tries to pull the version from the tarball URL, and GitHub's URL is different than npmjs (see below return of npm.pkg.github.com).
Here's an example of what happens on lookup:
And the component that gets created:
The return from npm.pkg.github.com:
So it will work initially, creating a component with an empty version, but will not be able to look up/create other versions because it supports only a null version.