python 2.7: "TypeError: Level not an integer or a valid string: None" from logging code

Starting loggerhead throws the following traceback:

Traceback (most recent call last):
  File "./serve-branches", line 30, in <module>
    main(sys.argv[1:])
  File "/home/mkanat/projects/loggerhead-fixes/loggerhead/loggerhead/main.py", line 152, in main
    app = make_app_for_config_and_path(config, path)
  File "/home/mkanat/projects/loggerhead-fixes/loggerhead/loggerhead/main.py", line 106, in make_app_for_config_and_path
    setup_logging(config)
  File "/home/mkanat/projects/loggerhead-fixes/loggerhead/loggerhead/main.py", line 62, in setup_logging
    logging.getLogger('').setLevel(log_level)
  File "/usr/lib64/python2.7/logging/__init__.py", line 1104, in setLevel
    self.level = _checkLevel(level)
  File "/usr/lib64/python2.7/logging/__init__.py", line 190, in _checkLevel
    raise TypeError("Level not an integer or a valid string: %r" % level)
TypeError: Level not an integer or a valid string: None