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/funnel_trends.py
{step_counts}
                ) GROUP BY entrance_period_start {breakdown_clause}
            ) data
            RIGHT OUTER JOIN (
                SELECT
                    {interval_method}(toDateTime('{self._filter.date_from.strftime(TIMESTAMP_FORMAT)}') + number * {seconds_in_interval}) AS entrance_period_start
                    {', breakdown_value as prop' if breakdown_clause else ''}
                FROM numbers({num_intervals}) AS period_offsets
                {'ARRAY JOIN (%(breakdown_values)s) AS breakdown_value' if breakdown_clause else ''}
            ) fill
            USING (entrance_period_start {breakdown_clause})
            ORDER BY entrance_period_start ASC
            SETTINGS allow_experimental_window_functions = 1"""
        return query
    def get_steps_reached_conditions(self) -> Tuple[str, str, str]:
        # Ho
        from_step = self._filter.funnel_from_step or 0
        # Ho
        to_step = self._filter.funnel_to_step or len(self._filter.entities) - 1
        # Th
        reached_from_step_count_condition = f"steps_completed >= {from_step+1}"
        # Th
        reached_to_step_count_condition = f"steps_completed >= {to_step+1}"
        # Th
        did_not_reach_to_step_count_condition = f"{reached_from_step_count_condition} AND steps_completed < {to_step+1}"
        return reached_from_step_count_condition, reached_to_step_count_condition, did_not_reach_to_step_count_condition
    def _summarize_data(self, results):
        breakdown_clause = self._get_breakdown_prop()
        summary = []
        for period_row in results: