Cannot add repository as a submodule if it does not have master branch

[fen-x]

Rugged::SubmoduleCollection#clone_submodule assumes that every repository has master branch. It is usually true but not generally correct. For instance xcode-test-engine for arc has only stable and develop, last one is default. That means I cannot add mentioned repository as a submodule using rugged.

I did a search and found an explanation of how git determines default branch to checkout after git clone.