Union[List[str], None]: Fields defining clustering for the table

        (Defaults to :data:`None`).

        Clustering fields are immutable after table creation.

        .. note::

           As of 2018-06-29, clustering fields cannot be set on a table
           which does not also have time partioning defined.

def clustering_fields(self):
        """Union[List[str], None]: Fields defining clustering for the table

        (Defaults to :data:`None`).

        Clustering fields are immutable after table creation.

        .. note::

           As of 2018-06-29, clustering fields cannot be set on a table
           which does not also have time partioning defined.
        """
        prop = self._properties.get("clustering")
        if prop is not None:
            return list(prop.get("fields", ()))