Enumerating a package that has variations that are both versioned and unversioned

[markfinal]

I think this is rare, but if you have a package, and it's varieties are as such

Package
Package-v1
Package-v2
...
Package-vN

such that the first one is unversioned (maybe tracking a head), but the remainder are versioned.

This causes package dependency resolution to fail badly in a null dereference.