🚨 Error: Cannot read property 'style' of null

Details
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**Error report:** [link](http://go/ampe/COC0l7X179DcLA)
**First seen:** Apr 15, 2020
**Frequency:** ~ 5,922/day

Stacktrace
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Error: Cannot read property 'style' of null

    at element (src/style.js:145:4)

    at getStyle (extensions/amp-ad-network-doubleclick-impl/0.1/safeframe-host.js:772:34)

    at onFluidResize_ (extensions/amp-ad-network-doubleclick-impl/0.1/safeframe-host.js:759:10)

Notes
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`@rsimha` modified `src/style.js:144-148` in #21212 (May 16, 2019)
`@glevitzky` modified `extensions/amp-ad-network-doubleclick-impl/0.1/safeframe-host.js:770-775` in #16393 (Jul 2, 2018)
`@glevitzky` modified `extensions/amp-ad-network-doubleclick-impl/0.1/safeframe-host.js:756-761` in #25414 (Nov 7, 2019)

**Seen in:**
- 08-29 Stable (0323+6)
- 09-19 Control (0410+2)
- 09-19 Stable (0410+2)
- 09-25 Beta (2320+1)
- 09-25 Experimental (2320+1)
- +7 more

**Possible assignees:** `@glevitzky`

/cc @ampproject/release-on-duty

Start with src/style.js:145 and extensions/amp-ad-network-doubleclick-impl/0.1/safeframe-host.js:759-772, then review the linked commits #21212, #16393, and #25414. Use the error report to investigate the null element in onFluidResize_; done means the reported style error no longer occurs in the affected path and the relevant behavior is covered by the project’s tests.

Written by the indexing model from the issue text.