./manage.py sync_templates --help fails with TypeError

[nschlemm]

using django 2.2 on python 3.7.3, expading the help text with %default fails with a traceback like:

./manage.py sync_templates --help
Traceback (most recent call last):
  File "./manage.py", line 21, in <module>
    main()
[...]
  File "/usr/local/lib/python3.7/argparse.py", line 525, in _format_action
    help_text = self._expand_help(action)
  File "/usr/local/lib/python3.7/argparse.py", line 614, in _expand_help
    return self._get_help_string(action) % params
TypeError: %d format: a number is required, not dict