Code review comment for lp:~danilo/maas/django-upgrade-legacy-migrations

I'm confused about how appending to INSTALLED_APPS is going to work. I see the following code in the file, when I look at the full diff context:

    # We expect the following settings to be overridden. They are mentioned here
    # to silence lint warnings.
    INSTALLED_APPS = None

    # Extend base settings.
    import_settings(settings)

    prevent_migrations = StringBool().to_python(
    os.environ.get("MAAS_PREVENT_MIGRATIONS", 0))

    if prevent_migrations:
        INSTALLED_APPS += ("maasserver.tests", "metadataserver.tests")

So how is a tuple going to be appended to None?