flatten.py error =[

mlustig-macbookpro:ud851-Sunshine mlustig$ git b
* master
mlustig-macbookpro:ud851-Sunshine mlustig$ git checkout sunshine-clean-history 
Branch sunshine-clean-history set up to track remote branch sunshine-clean-history from origin.
Switched to a new branch 'sunshine-clean-history'
mlustig-macbookpro:ud851-Sunshine mlustig$ git checkout --orphan student
Switched to a new branch 'student'
mlustig-macbookpro:ud851-Sunshine mlustig$ git branch -m sunshine-clean-history develop
mlustig-macbookpro:ud851-Sunshine mlustig$ git b
  develop
  master
mlustig-macbookpro:ud851-Sunshine mlustig$ flatten.py 
Removing local branch: master
Creating local branch: S03.02-Solution-RecyclerViewClickHandling
Traceback (most recent call last):
  File "/Users/mlustig/bin/flatten.py", line 141, in <module>
    sys.exit(main())
  File "/Users/mlustig/bin/flatten.py", line 138, in main
    flattener.flatten()
  File "/Users/mlustig/bin/flatten.py", line 44, in flatten
    self.create_local_branches()
  File "/Users/mlustig/bin/flatten.py", line 84, in create_local_branches
    new_branch = self.repo.create_head(branch_name)
  File "/Library/Python/2.7/site-packages/git/repo/base.py", line 338, in create_head
    return Head.create(self, path, commit, force, logmsg)
  File "/Library/Python/2.7/site-packages/git/refs/symbolic.py", line 527, in create
    return cls._create(repo, path, cls._resolve_ref_on_create, reference, force, logmsg)
  File "/Library/Python/2.7/site-packages/git/refs/symbolic.py", line 479, in _create
    target = repo.rev_parse(str(reference))
  File "/Library/Python/2.7/site-packages/git/repo/fun.py", line 311, in rev_parse
    obj = name_to_object(repo, rev)
  File "/Library/Python/2.7/site-packages/git/repo/fun.py", line 124, in name_to_object
    raise BadName(name)
gitdb.exc.BadName: Ref 'HEAD' did not resolve to an object