Sentry Issue: [POSTHOG-37H](https://sentry.io/organizations/posthog/issues/2511149053/?referrer=github_integration)

```
AttributeError: 'NoneType' object has no attribute 'strftime'
(3 additional frame(s) were not displayed)
...
  File "ee/clickhouse/views/insights.py", line 90, in calculate_funnel
    "result": ClickhouseFunnelTrends(team=team, filter=filter, funnel_order_class=funnel_order_class).run()
  File "ee/clickhouse/queries/funnels/base.py", line 48, in run
    results = self._exec_query()
  File "ee/clickhouse/queries/funnels/funnel_trends.py", line 61, in _exec_query
    return self._summarize_data(super()._exec_query())
  File "ee/clickhouse/queries/funnels/base.py", line 118, in _exec_query
    query = self.get_query()
  File "ee/clickhouse/queries/funnels/funnel_trends.py", line 112, in get_query
    {interval_method}(toDateTime('{self._filter.date_from.strftime(TIMESTAMP_FORMAT)}') + number * {seconds_in_interval}) AS entrance_period_start
```
ee/clickhouse/queries/funnels/test/test_funnel_trends.py
self.assertEqual(0, sunday["reached_to_step_count"])
        self.assertEqual(2, sunday["reached_from_step_count"])
        self.assertEqual(0, sunday["conversion_rate"])
        self.assertEqual(True, sunday["is_period_final"])
        monday = results[2]  
        self.assertEqual(0, monday["reached_to_step_count"])
        self.assertEqual(0, monday["reached_from_step_count"])
        self.assertEqual(0, monday["conversion_rate"])
        self.assertEqual(True, monday["is_period_final"])
        tuesday = results[3]  
        self.assertEqual(0, tuesday["reached_to_step_count"])
        self.assertEqual(0, tuesday["reached_from_step_count"])
        self.assertEqual(0, tuesday["conversion_rate"])
        self.assertEqual(True, tuesday["is_period_final"])
        wednesday = results[4]  
        self.assertEqual(0, wednesday["reached_to_step_count"])
        self.assertEqual(0, wednesday["reached_from_step_count"])
        self.assertEqual(0, wednesday["conversion_rate"])
        self.assertEqual(True, wednesday["is_period_final"])
        thursday = results[5]  
        self.assertEqual(0, thursday["reached_to_step_count"])
        self.assertEqual(1, thursday["reached_from_step_count"])
        self.assertEqual(0, thursday["conversion_rate"])
        self.assertEqual(True, thursday["is_period_final"])
        friday = results[6]  
        self.assertEqual(0, friday["reached_to_step_count"])
        self.assertEqual(0, friday["reached_from_step_count"])
        self.assertEqual(0, friday["conversion_rate"])
        self.assertEqual(True, friday["is_period_final"])
    def test_window_size_one_day(self):