fix: Fix treeForVendor failing
fix: Fix treeForVendor failing

It was failing because if there are no files in a tree, it's treeFor
receives no argument, instead of a tree. Turns out you can't mergeTrees
on undefined

brunopedroso/ember-hoodie,courajs/ember-hoodie,hoodiehq/ember-hoodie,courajs/ember-hoodie,brunopedroso/ember-hoodie,hoodiehq/ember-hoodie