Description of problem:
$ pulp-admin rpm repo create --repo-id=f18 --relative-url=f18 --feed=http://dl.fedoraproject.org/pub/fedora/linux/releases/18/Everything/x86_64/os/ --skip=rpm,drpm

run a sync on the above repo, and it fails when parsing groups with this traceback in pulp.log:

2013-06-28 11:16:49,762 pulp.server.managers.repo.sync:ERROR: Exception caught from plugin during sync for repo [f18]
Traceback (most recent call last):
  File "/home/mhrivnak/git/pulp/platform/src/pulp/server/managers/repo/sync.py", line 155, in _do_sync
    sync_report = importer_instance.sync_repo(transfer_repo, conduit, call_config)
  File "/home/mhrivnak/git/pulp_rpm/plugins/pulp_rpm/plugins/importers/yum/importer.py", line 88, in sync_repo
    return self._current_sync.run()
  File "/home/mhrivnak/git/pulp_rpm/plugins/pulp_rpm/plugins/importers/yum/sync.py", line 141, in run
    self.get_groups(metadata_files)
  File "/home/mhrivnak/git/pulp_rpm/plugins/pulp_rpm/plugins/importers/yum/sync.py", line 441, in get_groups
    self.save_fileless_units(group_file_handle, group.GROUP_TAG, process_func)
  File "/home/mhrivnak/git/pulp_rpm/plugins/pulp_rpm/plugins/importers/yum/sync.py", line 485, in save_fileless_units
    to_save = existing.check_repo(wanted, self.sync_conduit.get_units)
  File "/home/mhrivnak/git/pulp_rpm/plugins/pulp_rpm/plugins/importers/yum/existing.py", line 36, in check_repo
    sorted_units = _sort_by_type(wanted)
  File "/home/mhrivnak/git/pulp_rpm/plugins/pulp_rpm/plugins/importers/yum/existing.py", line 71, in _sort_by_type
    for unit in wanted:
  File "/home/mhrivnak/git/pulp_rpm/plugins/pulp_rpm/plugins/importers/yum/sync.py", line 483, in <genexpr>
    wanted = (model.as_named_tuple for model in package_info_generator)
  File "/home/mhrivnak/git/pulp_rpm/plugins/pulp_rpm/plugins/importers/yum/repomd/packages.py", line 74, in package_list_generator
    package_info = process_func(element)
  File "/home/mhrivnak/git/pulp_rpm/plugins/pulp_rpm/plugins/importers/yum/repomd/group.py", line 61, in process_group_element
    'user_visible': _parse_bool(element.find('uservisible').text),
AttributeError: 'NoneType' object has no attribute 'text'


We are having to guess at what we can expect to be in these XML files with hints from what yum itself looks for, so perhaps we are falsely assuming that the "uservisible" element is always present.