🚨 Error: Cannot read properties of null (reading 'next')

Details
---
**Error report:** [link](http://go/ampe/CMCn4cCn4qy1dw)
**First seen:** Sep 30, 2021
**Frequency:** ~ 12,210/day

Stacktrace
---

Error: Cannot read properties of null (reading 'next')

    at next (extensions/amp-story/1.0/amp-story.js:1287:15)

    at next_ (extensions/amp-story/1.0/amp-story.js:1366:11)

    at performTapNavigation_ (extensions/amp-story/1.0/amp-story.js:700:11)

    at navigationListener (extensions/amp-story/1.0/page-advancement.js:229:6)

    at forEach (extensions/amp-story/1.0/page-advancement.js:228:33)

    at onTapNavigation (extensions/amp-story/1.0/page-advancement.js:736:9)

Notes
---
`@prateekbh` modified `extensions/amp-story/1.0/page-advancement.js:229-232` in [#12671](https://github.com/ampproject/amphtml/pull/12671) (Jan 12, 2018)
`@renovate-bot` modified `extensions/amp-story/1.0/page-advancement.js:228-228` in [#27350](https://github.com/ampproject/amphtml/pull/27350) (Mar 30, 2020)
`@Enriqe` modified `extensions/amp-story/1.0/page-advancement.js:736-738` in [#16381](https://github.com/ampproject/amphtml/pull/16381) (Jun 29, 2018)

**Seen in:**
- 07-28 Stable (1718+2)
- 08-05 Beta (1912+1)
- 08-05 Control (1912+1)
- 08-05 Experiment-B (1912+1)
- 08-05 Nightly-Control (1912+1)
- 08-05 Stable (1912+1)
- +7 more

**Possible assignees:** `@Enriqe`, `@prateekbh`

/cc @ampproject/release-on-duty