🚨 Error: undefined is not an object (evaluating 'a.document.createEvent')

Details
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**Error report:** [link](http://go/ampe/CJnvj9a35MWd3AE)
**First seen:** Oct 17, 2021
**Frequency:** ~ 20,648/day

Stacktrace
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Error: undefined is not an object (evaluating 'a.document.createEvent')

    at createEvent (src/utils/event-helper.js:30:27)

    at a (extensions/amp-position-observer/0.1/amp-position-observer.js:165:4)

    at triggerScroll_ (extensions/amp-position-observer/0.1/amp-position-observer.js:233:6)

    at position (src/service/position-observer/position-observer-worker.js:97:20)

Notes
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`@choumx` modified `src/utils/event-helper.js:28-31` in [#8345](https://github.com/ampproject/amphtml/pull/8345) (Mar 24, 2017)
`@rsimha` modified `extensions/amp-position-observer/0.1/amp-position-observer.js:164-171` in [#21212](https://github.com/ampproject/amphtml/pull/21212) (May 16, 2019)
`@aghassemi` modified `extensions/amp-position-observer/0.1/amp-position-observer.js:233-233` in [#20915](https://github.com/ampproject/amphtml/pull/20915) (Feb 25, 2019)
`@zhouyx` modified `src/service/position-observer/position-observer-worker.js:94-124` in [#10813](https://github.com/ampproject/amphtml/pull/10813) (Sep 8, 2017)

**Seen in:**
- 10-08 Stable (2201+1)
- 10-08 Stable (2201+2)

**Possible assignees:** `@aghassemi`, `@zhouyx`

/cc @ampproject/release-on-duty