Traceback (most recent call last):
  File "/home/morane/.venv/lib/python3.5/site-packages/sphinx/config.py", line 161, in __init__
    execfile_(filename, config)
  File "/home/morane/.venv/lib/python3.5/site-packages/sphinx/util/pycompat.py", line 150, in execfile_
    exec_(code, _globals)
  File "conf.py", line 6, in <module>
    django.setup()
  File "/home/morane/.venv/lib/python3.5/site-packages/django/__init__.py", line 24, in setup
    apps.populate(settings.INSTALLED_APPS)
  File "/home/morane/.venv/lib/python3.5/site-packages/django/apps/registry.py", line 112, in populate
    app_config.import_models()
  File "/home/morane/.venv/lib/python3.5/site-packages/django/apps/config.py", line 198, in import_models
    self.models_module = import_module(models_module_name)
  File "/usr/lib/python3.5/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 986, in _gcd_import
  File "<frozen importlib._bootstrap>", line 969, in _find_and_load
  File "<frozen importlib._bootstrap>", line 958, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 673, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 673, in exec_module
  File "<frozen importlib._bootstrap>", line 222, in _call_with_frames_removed
  File "/home/morane/Documents/code/swh-environment/swh-deposit/swh/deposit/models.py", line 94, in <module>
    class Deposit(models.Model):
  File "/home/morane/Documents/code/swh-environment/swh-deposit/swh/deposit/models.py", line 118, in Deposit
    parent = models.ForeignKey('self', null=True)
TypeError: __init__() missing 1 required positional argument: 'on_delete'

../../swh-docs/Makefile.sphinx:34: recipe for target 'sphinx/html' failed
make: *** [sphinx/html] Error 2