~/Documents/gerrit/integration/quibble$ pip3 freeze|grep -i GitPython
GitPython==2.1.1

~/Documents/gerrit/integration/quibble$ git --version
git version 2.15.1 (Apple Git-101)

~/Documents/gerrit/integration/quibble$ quibble
DEBUG:quibble.cmd:Running stages: all
INFO:quibble.cmd:Adding mediawiki/vendor
INFO:quibble.cmd:Projects: mediawiki/core, mediawiki/skins/Vector, mediawiki/vendor
INFO:zuul.CloneMapper:Workspace path set to: /Users/z/Documents/gerrit/integration/quibble/src
INFO:zuul.CloneMapper:Mapping projects to workspace...
INFO:zuul.CloneMapper:  mediawiki/core -> /Users/z/Documents/gerrit/integration/quibble/src
INFO:zuul.CloneMapper:  mediawiki/skins/Vector -> /Users/z/Documents/gerrit/integration/quibble/src/skins/Vector
INFO:zuul.CloneMapper:  mediawiki/vendor -> /Users/z/Documents/gerrit/integration/quibble/src/vendor
DEBUG:zuul.CloneMapper:Checking overlap in destination directories...
INFO:zuul.CloneMapper:Expansion completed.
INFO:zuul.Cloner:Preparing 3 repositories
INFO:zuul.Cloner:Creating repo mediawiki/core from upstream https://gerrit.wikimedia.org/r/p/mediawiki/core
DEBUG:zuul.Repo:Resetting repository /Users/z/Documents/gerrit/integration/quibble/src
DEBUG:zuul.Repo:Updating repository /Users/z/Documents/gerrit/integration/quibble/src
Traceback (most recent call last):
  File "/usr/local/bin/quibble", line 11, in <module>
    load_entry_point('quibble', 'console_scripts', 'quibble')()
  File "/Users/z/Documents/gerrit/integration/quibble/quibble/cmd.py", line 405, in main
    cmd.execute()
  File "/Users/z/Documents/gerrit/integration/quibble/quibble/cmd.py", line 300, in execute
    self.clone(projects_to_clone)
  File "/Users/z/Documents/gerrit/integration/quibble/quibble/cmd.py", line 142, in clone
    cache_dir=self.args.git_cache)
  File "/Users/z/Documents/gerrit/integration/quibble/quibble/zuul.py", line 47, in clone
    return zuul_cloner.execute()
  File "/Users/z/Documents/gerrit/integration/quibble/zuul/lib/cloner.py", line 75, in execute
    self.prepareRepo(project, dest)
  File "/Users/z/Documents/gerrit/integration/quibble/zuul/lib/cloner.py", line 169, in prepareRepo
    repo.reset()
  File "/Users/z/Documents/gerrit/integration/quibble/zuul/merger/merger.py", line 102, in reset
    for ref in origin.refs:
  File "/usr/local/lib/python3.6/site-packages/git/remote.py", line 527, in refs
    out_refs.extend(RemoteReference.list_items(self.repo, remote=self.name))
  File "/usr/local/lib/python3.6/site-packages/git/util.py", line 932, in list_items
    out_list.extend(cls.iter_items(repo, *args, **kwargs))
  File "/usr/local/lib/python3.6/site-packages/git/refs/symbolic.py", line 592, in _iter_items
    for sha, rela_path in cls._iter_packed_refs(repo):  # @UnusedVariable
  File "/usr/local/lib/python3.6/site-packages/git/refs/symbolic.py", line 92, in _iter_packed_refs
    raise TypeError("PackingType of packed-Refs not understood: %r" % line)
TypeError: PackingType of packed-Refs not understood: '# pack-refs with: peeled fully-peeled sorted'