fix: address review comments.

Author: mariamjamal94

optimizely/event/event_processor.py

@@ -95,6 +95,10 @@ def __init__(self,
     self.notification_center = notification_center
     self._current_batch = list()
 
+    if not validator.is_notification_center_valid(self.notification_center):
+      self.logger.error(enums.Errors.INVALID_INPUT.format('notification_center'))
+      self.notification_center = notification_center.NotificationCenter()
+
     if start_on_init is True:
       self.start()
 

tests/test_event_processor.py

@@ -376,7 +376,7 @@ def test_init__NaN_timeout_interval(self):
     self.assertEqual(self._event_processor.timeout_interval, timedelta(seconds=5))
     mock_config_logging.info.assert_called_with('Using default value for timeout_interval.')
 
-  def test_notification_center(self):
+  def test_notification_center__on_log_event(self):
 
     mock_event_dispatcher = mock.Mock()
     callback_hit = [False]