def _get_field(self, f, default=None):
        """
        Fetches a field from extras, and returns it. This is some Airflow
        magic. The google_cloud_platform hook type adds custom UI elements
        to the hook page, which allow admins to specify service_account,
        key_path, etc. They get formatted as shown below.
        """
        long_f = 'extra__google_cloud_platform__{}'.format(f)
        if hasattr(self, 'extras') and long_f in self.extras:
            return self.extras[long_f]
        else:
            return default
Fetches a field from extras, and returns it. This is some Airflow
        magic. The google_cloud_platform hook type adds custom UI elements
        to the hook page, which allow admins to specify service_account,
        key_path, etc. They get formatted as shown below.