Cannot migrate branches rather than master

[kutluhanmetin]

In the documentation it says:

So if the subrepo is foo.git and it contains a branch whatever, in the monorepo the SHA pointed to by the branch whatever in the original repo will now be pointed to by a branch named foo/whatever.

however it just migrates master branches.

Ex.
Source repository repo1 has branches: branch1, branch2, master
Source repository repo2 has branches: branch3, branch4, master
And something.repos includes repo1 and repo2

Actual behaviour:
After running ./build something.repos,
git branch -a prints:
master
repo1/master
repo2/master

Expected behaviour:
After running ./build something.repos,
git branch -a should print:
master
repo1/master
repo2/master
repo1/branch1
repo1/branch2
repo2/branch3
repo2/branch4