"You are on a branch yet to be born" when adding git submodule

Question

To fix that error, you should delete the folder with the same path to the submodule inside .git/modules/ directory. This error can occurs when url was incorrect for submodule for the first-time when submodule was added.

This error can happen if you are adding a submodule which doesn't have a master branch. If you want to use another branch when adding the submodule (develop for instance), you can use the following command:

git submodule add -b <branch> <repository>

You need to add a submodule inside an existing repo, that repo needs to be in a state to add & commit the submodule link, and the submodule repo itself must have a commit to check out.

Now, the submodule repo itself must be ok if you can create a regular clone elsewhere. However, it looks like submodule add complains if the repo is empty while clone does not. This guy suggests this is fixable by just running the same submodule add command again.

If the inner repo is not empty, check the repo you want to contain the submodule. Change to the same directory where you ran git submodule add, and run git status, and git branch to verify that your containing repo has at least one branch created and isn't in a weird state.