Traceback (most recent call last):
  File "<console>", line 1, in <module>
  File "/home/vaka_waka/projects/some_project_wagtail/.venv/lib/python3.6/site-packages/django/forms/forms.py", line 180, in errors
    self.full_clean()
  File "/home/vaka_waka/projects/some_project_wagtail/.venv/lib/python3.6/site-packages/django/forms/forms.py", line 381, in full_clean
    self._clean_fields()
  File "/home/vaka_waka/projects/some_project_wagtail/.venv/lib/python3.6/site-packages/django/forms/forms.py", line 393, in _clean_fields
    value = field.widget.value_from_datadict(self.data, self.files, self.add_prefix(name))
  File "/home/vaka_waka/projects/some_project_wagtail/.venv/lib/python3.6/site-packages/wagtail/admin/rich_text/editors/draftail/__init__.py", line 70, in value_from_datadict
    return self.converter.to_database_format(original_value)
  File "/home/vaka_waka/projects/some_project_wagtail/.venv/lib/python3.6/site-packages/wagtail/admin/rich_text/converters/contentstate.py", line 90, in to_database_format
    return self.exporter.render(json.loads(contentstate_json))
  File "/usr/lib/python3.6/json/__init__.py", line 354, in loads
    return _default_decoder.decode(s)
  File "/usr/lib/python3.6/json/decoder.py", line 339, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
  File "/usr/lib/python3.6/json/decoder.py", line 357, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None