Why does leapp preupgrade command fail with error "ModelViolationError: The value of "name" field is None, but this is not allowed"?

Issue

• The leapp preupgrade command is failing with the following error.

  # leapp preupgrade
   Process Process-206:
   Traceback (most recent call last):
     File "/usr/lib64/python2.7/multiprocessing/process.py", line 258, in _bootstrap
       self.run()
     File "/usr/lib64/python2.7/multiprocessing/process.py", line 114, in run
       self._target(*self._args, **self._kwargs)
     File "/usr/lib/python2.7/site-packages/leapp/repository/actor_definition.py", line 72, in _do_run
       actor_instance.run(*args, **kwargs)
     File "/usr/lib/python2.7/site-packages/leapp/actors/__init__.py", line 290, in run
       self.process(*args)
     File "/usr/share/leapp-repository/repositories/system_upgrade/common/actors/scansubscriptionmanagerinfo/actor.py", line 21, in process
       scanrhsm.scan()
     File "/usr/share/leapp-repository/repositories/system_upgrade/common/libraries/rhsm.py", line 103, in wrapper
       return f(*args, **kwargs)
     File "/usr/share/leapp-repository/repositories/system_upgrade/common/actors/scansubscriptionmanagerinfo/libraries/scanrhsm.py", line 9, in scan
       info = rhsm.scan_rhsm_info(context)
     File "/usr/share/leapp-repository/repositories/system_upgrade/common/libraries/rhsm.py", line 103, in wrapper
       return f(*args, **kwargs)
     File "/usr/share/leapp-repository/repositories/system_upgrade/common/libraries/rhsm.py", line 382, in scan_rhsm_info
       info.available_repos = get_available_repo_ids(context)
     File "/usr/share/leapp-repository/repositories/system_upgrade/common/libraries/rhsm.py", line 171, in get_available_repo_ids
       repofiles = repofileutils.get_parsed_repofiles(context)
     File "/usr/share/leapp-repository/repositories/system_upgrade/common/libraries/repofileutils.py", line 77, in get_parsed_repofiles
       repofile = parse_repofile(context.full_path(repofile_path))
     File "/usr/share/leapp-repository/repositories/system_upgrade/common/libraries/repofileutils.py", line 41, in parse_repofile
       data.append(_parse_repository(repoid, dict(cp.items(repoid))))
     File "/usr/share/leapp-repository/repositories/system_upgrade/common/libraries/repofileutils.py", line 26, in _parse_repository
       return RepositoryData(**prepared)
     File "/usr/lib/python2.7/site-packages/leapp/models/__init__.py", line 88, in __init__
       getattr(defined_fields[field], init_method)(kwargs, field, self)
     File "/usr/lib/python2.7/site-packages/leapp/models/fields/__init__.py", line 110, in from_initialization
       self._validate_model_value(value=source_value, name=name)
     File "/usr/lib/python2.7/site-packages/leapp/models/fields/__init__.py", line 179, in _validate_model_value
       super(BuiltinField, self)._validate_model_value(value, name)
     File "/usr/lib/python2.7/site-packages/leapp/models/fields/__init__.py", line 60, in _validate_model_value
       raise ModelViolationError('The value of "{name}" field is None, but this is not allowed'.format(name=name))
   ModelViolationError: The value of "name" field is None, but this is not allowed