[cupertino_ui] Remove redundant null arguments in Completer.complete - #13008

…utter#193718)

This is work towards dart-lang/sdk#59150

The lint rule `avoid_redundant_argument_values` is being updated
(https://dart-review.googlesource.com/c/sdk/+/491341) to also flag
redundant `null` arguments passed to optional parameters whose default
value is `null` (such as `Completer<void>.complete(null)`).

Already merged "upstream" at
flutter/packages#13008

## Pre-launch Checklist

- [x] I read the [Contributor Guide] and followed the process outlined
there for submitting PRs.
- [x] I read the [AI contribution guidelines] and understand my
responsibilities, or I am not using AI tools.
- [x] I read the [Tree Hygiene] wiki page, which explains my
responsibilities.
- [x] I read and followed the [Flutter Style Guide], including [Features
we expect every widget to implement].
- [x] I signed the [CLA].
- [x] I listed at least one issue that this PR fixes in the description
above.
- [x] I updated/added relevant in-code documentation (doc comments with
`///`).
- [x] If this PR introduces a new feature or capability, I created and
linked a website documentation issue or PR in [flutter/website] (or
verified none is needed).
- [x] I added new tests to check the change I am making, or this PR is
[test-exempt].
- [x] I followed the [breaking change policy] and added [Data Driven
Fixes] where supported.
- [x] All existing and new tests are passing.

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…er#193840)

flutter/packages@5620e65...951f2f7

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(flutter/packages#13058)
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2026-10-02 [email protected] [cupertino_ui]
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(flutter/packages#13029)
2026-10-02 [email protected] [ci] Add material_ui and cupertino_ui
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2026-10-02 [email protected] [material_ui]
Remove unconditional dart:io import from about.dart
(flutter/packages#12774)
2026-10-02 [email protected] [material_ui] Fix
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(flutter/packages#12606)
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2026-10-02 [email protected]
[url_launcher] Fix supportsCloseForLaunchMode to query close support
(flutter/packages#12926)
2026-10-02 [email protected] Redistribute
iOS/macOS Suggested Reviewers (flutter/packages#13076)
2026-10-02 [email protected] [image_picker] Subsample large images
when resizing on Android (flutter/packages#13038)
2026-10-02 [email protected] [cupertino_ui] Remove
redundant null arguments in Completer.complete (flutter/packages#13008)
2026-10-02 [email protected] [repo]
Update AGENTS.md with dependency allowance and versioning guidance
(flutter/packages#12579)

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