DjangoのSECRET_KEYを隠すことについて

前提・実現したいこと

DjangoでSECRET_KEYを隠したいと思っています。
SECRET_KEYを置いておく、local_settings.pyを作成して、settinds.pyに
from .local_settings import *　
でインポートし、Herokuでマイグレーションするとエラーが発生してしまいました。

発生している問題・エラーメッセージ

heroku run python manage.py makemigrations


File "/app/config/settings.py", line 18, in <module>
    from .local_settings import *
ModuleNotFoundError: No module named 'config.local_settings'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "manage.py", line 22, in <module>
    main()
  File "manage.py", line 18, in main
    execute_from_command_line(sys.argv)
  File "/app/.heroku/python/lib/python3.6/site-packages/django/core/management/__init__.py", line 401, in execute_from_command_line
    utility.execute()
  File "/app/.heroku/python/lib/python3.6/site-packages/django/core/management/__init__.py", line 395, in execute
    self.fetch_command(subcommand).run_from_argv(self.argv)
  File "/app/.heroku/python/lib/python3.6/site-packages/django/core/management/base.py", line 343, in run_from_argv
    connections.close_all()
  File "/app/.heroku/python/lib/python3.6/site-packages/django/db/utils.py", line 232, in close_all
    for alias in self:
  File "/app/.heroku/python/lib/python3.6/site-packages/django/db/utils.py", line 226, in __iter__
    return iter(self.databases)
  File "/app/.heroku/python/lib/python3.6/site-packages/django/utils/functional.py", line 48, in __get__
    res = instance.__dict__[self.name] = self.func(instance)
  File "/app/.heroku/python/lib/python3.6/site-packages/django/db/utils.py", line 153, in databases
    self._databases = settings.DATABASES
  File "/app/.heroku/python/lib/python3.6/site-packages/django/conf/__init__.py", line 83, in __getattr__
    self._setup(name)
  File "/app/.heroku/python/lib/python3.6/site-packages/django/conf/__init__.py", line 70, in _setup
    self._wrapped = Settings(settings_module)
  File "/app/.heroku/python/lib/python3.6/site-packages/django/conf/__init__.py", line 177, in __init__
    mod = importlib.import_module(self.SETTINGS_MODULE)
  File "/app/.heroku/python/lib/python3.6/importlib/__init__.py", line 126, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 994, in _gcd_import
  File "<frozen importlib._bootstrap>", line 971, in _find_and_load
  File "<frozen importlib._bootstrap>", line 955, in _find_and_load_unlocked
  File "<frozen importlib._bootstrap>", line 665, in _load_unlocked
  File "<frozen importlib._bootstrap_external>", line 678, in exec_module
  File "<frozen importlib._bootstrap>", line 219, in _call_with_frames_removed
  File "/app/config/settings.py", line 18, in <module>
    from .local_settings import *
ModuleNotFoundError: No module named 'config.local_settings'

該当のソースコード

#settings.pyより

from .local_settings import *


#local_settingsには
SECRET_KEY = 'hogehoge'
と書いてあります。

試したこと

settings.pyに以下のコードを追加しました。


import json

# Normally you should not import ANYTHING from Django directly
# into your settings, but ImproperlyConfigured is an exception.
from django.core.exceptions import ImproperlyConfigured

# JSON-based secrets module
with open("secrets.json") as f:
    secrets = json.loads(f.read())

def get_secret(setting, secrets=secrets):
    """Get the secret variable or return explicit exception."""
    try:
        return secrets[setting]
    except KeyError:
        error_msg = "Set the {0} environment variable".format(setting)
        raise ImproperlyConfigured(error_msg)

SECRET_KEY = get_secret("SECRET_KEY")

secrets.jsonを作成して以下のコードを書きました。
{
    "FILENAME": "secrets.json",
    "SECRET_KEY": "hogehoge"
}