fail to execute firstly when there is no container

[mkouhei]

$ bu2sw -c bu2sw.conf -l
Traceback (most recent call last):
  File "/usr/bin/bu2sw", line 9, in <module>
    load_entry_point('backup2swift==0.1', 'console_scripts', 'bu2sw')()
  File "/usr/lib/python2.7/dist-packages/backup2swift/command.py", line 82, in main
    args.func(args)
  File "/usr/lib/python2.7/dist-packages/backup2swift/command.py", line 72, in execute_swift_client
    backup_l = b.retrieve_backup_data_list(args.verbose)
  File "/usr/lib/python2.7/dist-packages/backup2swift/backup.py", line 133, in retrieve_backup_data_list
    self.container_name)]
TypeError: 'NoneType' object is not iterable

$ bu2sw -c bu2sw.conf -p $(pwd)
Traceback (most recent call last):
  File "/usr/bin/bu2sw", line 9, in <module>
    load_entry_point('backup2swift==0.1', 'console_scripts', 'bu2sw')()
  File "/usr/lib/python2.7/dist-packages/backup2swift/command.py", line 82, in main
    args.func(args)
  File "/usr/lib/python2.7/dist-packages/backup2swift/command.py", line 76, in execute_swift_client
    b.backup(args.path)
  File "/usr/lib/python2.7/dist-packages/backup2swift/backup.py", line 43, in backup
    [self.backup_file(f) for f in glob.glob(target_path + '/*')]
  File "/usr/lib/python2.7/dist-packages/backup2swift/backup.py", line 70, in backup_file
    self.container_name)]
TypeError: 'NoneType' object is not iterable