Fyi, when trying to copy a package to another repository using the Copy button,
it presented a list of repositories to which I selected the last one and then
got this error.

I traced the problem down to MCVersionInspector>>#pickRepository being
incompatible with any repository type whose #description consumes more than one
line.  In that case, the array index selection from the menu doesn't match the
index into the repositories list.

Ahh, I see this is for my own repository type (Magma), so I'll fix its
#description to be all on one line.  Sneaky!

 - Chris