Fixed #22645: Allow apps with no models module to still have migrations

from __future__ import unicode_literals

from importlib import import_module

        self.unmigrated_apps = set()

        self.migrated_apps = set()

        for app_config in apps.get_app_configs():

            if app_config.models_module is None:

                continue

            # Get the migrations module directory

            module_name = self.migrations_module(app_config.label)

            was_loaded = module_name in sys.modules