code: def default_dataset(self):
          
          prop = self._get_sub_prop("defaultDataset")
          if prop is not None:
              prop = DatasetReference.from_api_repr(prop)
          return prop
docs: google.cloud.bigquery.dataset.DatasetReference: the default dataset
          to use for unqualified table names in the query or :data:`None` if not
          set.
  
          The ``default_dataset`` setter accepts:
  
          - a :class:`~google.cloud.bigquery.dataset.Dataset`, or
          - a :class:`~google.cloud.bigquery.dataset.DatasetReference`, or
          - a :class:`str` of the fully-qualified dataset ID in standard SQL
            format. The value must included a project ID and dataset ID
            separated by ``.``. For example: ``your-project.your_dataset``.
  
          See
          https://g.co/cloud/bigquery/docs/reference/v2/jobs#configuration.query.defaultDataset