Throws an exception if assets file is not configured or cannot be found.
        :param assets: path to the assets file

def check_assets(self):
        """
        Throws an exception if assets file is not configured or cannot be found.
        :param assets: path to the assets file
        """
        if not self.assets_file:
            raise ImproperlyConfigured("You must specify the path to the assets.json file via WEBPACK_ASSETS_FILE")
        elif not os.path.exists(self.assets_file):
            raise ImproperlyConfigured(
                "The file `{file}` was not found, make sure to run the webpack build before the collectstatic command".format(
                    file=self.assets_file))