docstr: Run the nth empty ingest.
  
  Returns
  -------
  wrote_to : str
      The timestr of the bundle written.
code: def _empty_ingest(self, _wrote_to=[]):
      """Run the nth empty ingest.
  
      Returns
      -------
      wrote_to : str
          The timestr of the bundle written.
      """
      if not self.bundles:
  
          @self.register(
              "bundle",
              calendar_name="NYSE",
              start_session=pd.Timestamp("2014", tz="UTC"),
              end_session=pd.Timestamp("2014", tz="UTC"),
          )
          def _(
              environ,
              asset_db_writer,
              minute_bar_writer,
              daily_bar_writer,
              adjustment_writer,
              calendar,
              start_session,
              end_session,
              cache,
              show_progress,
              output_dir,
          ):
              _wrote_to.append(output_dir)
  
      _wrote_to[:] = []
      self.ingest("bundle", environ=self.environ)
      assert_equal(
          len(_wrote_to), 1, msg="ingest was called more than once"
      )
      ingestions = self._list_bundle()
      assert_in(
          _wrote_to[0],
          ingestions,
          msg="output_dir was not in the bundle directory",
      )
      return _wrote_to[0]
  
imports: import os
  from nose_parameterized import parameterized
  import pandas
  import sqlalchemy
  from toolz import valmap
  import toolz.curried.operator
  from trading_calendars import TradingCalendar, get_calendar
  from zipline.assets import ASSET_DB_VERSION
  from zipline.assets.asset_writer import check_version_info
  from zipline.assets.synthetic import make_simple_equity_info
  from zipline.data.bundles import UnknownBundle, from_bundle_ingest_dirname, ingestions_for_bundle
  from zipline.data.bundles.core import _make_bundle_core, BadClean, to_bundle_ingest_dirname, asset_db_path
  from zipline.lib.adjustment import Float64Multiply
  from zipline.pipeline.loaders.synthetic import make_bar_data, expected_bar_values_2d
  from zipline.testing import subtest, str_to_seconds
  from zipline.testing.fixtures import WithInstanceTmpDir, ZiplineTestCase, WithDefaultDateBounds
  from zipline.testing.predicates import assert_equal, assert_false, assert_in, assert_is, assert_is_instance, assert_is_none, assert_raises, assert_true
  from zipline.utils.cache import dataframe_cache
  from zipline.utils.functional import apply
  import zipline.utils.paths
label_desc: Use image node_id 11 for calling the BundleCoreTestCase obj's underlying member method code with example usage: obj._empty_ingest(_wrote_to) and returns: _wrote_to