I am trying to use gitlab-backup to backup a set of repositories I created on a fresh gitlab instance. With my user ('root'), I created 3 git repo, but I didn't commited anything in any of them.

Running gitlab-backup pull gave:

 * Dumping gitlab data (except repositories & db)
Dumping database ...
[SKIPPED]
[...]
 Deleting old backups ... skipping
 * Unpacking dump tarballs
 * Dumping database
 * git-backup pull everything
# creating root commit
# file gitlab/misc      <- /srv/slapgrid/slappart18/srv/runner/instance/slappart0/backup-gitlab.git/gitlab-backup.kvR8EE/gitlab_backup/artifacts.tar.gz/.gitlab-backup-keep
# file gitlab/misc      <- /srv/slapgrid/slappart18/srv/runner/instance/slappart0/backup-gitlab.git/gitlab-backup.kvR8EE/gitlab_backup/backup_information.yml
# file gitlab/misc      <- /srv/slapgrid/slappart18/srv/runner/instance/slappart0/backup-gitlab.git/gitlab-backup.kvR8EE/gitlab_backup/builds.tar.gz/.gitlab-backup-keep
# file gitlab/misc      <- /srv/slapgrid/slappart18/srv/runner/instance/slappart0/backup-gitlab.git/gitlab-backup.kvR8EE/gitlab_backup/db/database.pgdump/2841.dat/2841.dat.aa 
[...]
# file gitlab/repo      <- /srv/slapgrid/slappart18/srv/runner/instance/slappart0/var/repositories/root/project3.wiki.git/description
# file gitlab/repo      <- /srv/slapgrid/slappart18/srv/runner/instance/slappart0/var/repositories/root/project3.wiki.git/hooks
# file gitlab/repo      <- /srv/slapgrid/slappart18/srv/runner/instance/slappart0/var/repositories/root/project3.wiki.git/info/exclude
cmd_pull: raisef: refs/backup/20161103-0924/: strange for-each-ref entry ""

and git log in the backup repo:

commit 6333abdb5e39a004b1a1db21b35db1e5235ed46c
Author: iv <isabelle.vallet@nexedi.com>
Date:   Thu Nov 3 09:24:41 2016 +0000

    Initialize git-backup repository

After I commited something (and removed current locked backup repo), it went all fine. After that, I added an empty repo, and it went all fine as well.