I checked out mpiwrappers with
 fedpkg clone -B mpiwrappers
and copied the sources (the spec and two text files) to mpiwrappers/master.

fedpkg commit resulted in

 3 files changed, 161 insertions(+), 0 deletions(-)
 create mode 100644 mpiwrappers.module
 create mode 100644 mpiwrappers.rpmmacro
 create mode 100644 mpiwrappers.spec
Traceback (most recent call last):
  File "/usr/bin/fedpkg", line 1086, in <module>
    args.command(args)
  File "/usr/bin/fedpkg", line 439, in commit
    push(args)
  File "/usr/bin/fedpkg", line 593, in push
    mymodule = pyfedpkg.PackageModule(args.path)
  File "/usr/lib/python2.6/site-packages/pyfedpkg/__init__.py", line 938, in __init__
    self.distval = self._findmasterbranch()
  File "/usr/lib/python2.6/site-packages/pyfedpkg/__init__.py", line 886, in _findmasterbranch
    return(int(fedoras[-1].strip('f')) + 1)
IndexError: list index out of range


after which a retry resulted in

# On branch master
# Your branch is ahead of 'origin/master' by 1 commit.
#
nothing to commit (working directory clean)
Could not commit: Command '['git', 'commit', '-m', 'Import package.', '-a']' returned non-zero exit status 1

Then I ran git commit, which succeded. Now when I try fedpkg build it gives me the same _findmasterbranch error as in the first traceback.