docstr: AlertPublisher - AlertPublisherRepository - assemble() - String
docstr_tok: ["AlertPublisher","-","AlertPublisherRepository","-","assemble","(",")","-","String"]
code: def test_assemble_alert_publisher_for_output_none(self):
      """AlertPublisher - AlertPublisherRepository - assemble() - String"""
      self._alert.publishers = None
  
      publisher = _assemble_alert_publisher_for_output(
          self._alert, self._output, self._descriptor
      )
  
      assert_true(isinstance(publisher, DefaultPublisher))
  
imports: from mock import patch
  from nose.tools import assert_true, assert_equal, assert_false
  from streamalert.alert_processor.helpers import _assemble_alert_publisher_for_output
  from streamalert.shared.publisher import AlertPublisherRepository, AlertPublisher, CompositePublisher, DefaultPublisher, Register, WrappedFunctionPublisher
  from tests.unit.streamalert.alert_processor.helpers import get_alert
label_desc: Use image node_id 2 for calling the TestAlertPublisherRepositoryAssemblePublisher obj's underlying member method code with example usage: obj.test_assemble_alert_publisher_for_output_none() without return types