Trying to checkout from a non-existing git branch gives the following error message:
fatal: git checkout: updating paths is incompatible with switching branches.
GetComponents gives an error, but only for the first link into such a repository, and the directories and links are also there after the checkout - but not of any other than the master branch. If someone overlooks the error at the end, a full and possibly working configuration could be built, but it would use the wrong version of the git repo. GetComponents should not checkout repositories if the given branch was not found, even with error message at the end. (updating by rerunning GetComponents later doesn't show this difference in braches as well, only indicating that all is there and well).
It would be nice (but not important, if too complicated), if a better message could be given in this case.