[Backport 2.x] Call 'toArray()' with an empty array instead of a pre-sized array

[andrross]

Backports 9fc3f4096958159ec9b53012fc7ced19fd793e1b from #5277 to 2.x

Check List

• [x] Functionality includes testing.
• [ ] ~API changes companion pull request created, if applicable.~
• [ ] ~Public documentation issue/PR created, if applicable.~

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[github-actions[bot]]

:x: Gradle check result for d79340f2d1ae7381800244578ecc4d2d58cf5412: FAILURE

Please examine the workflow log, locate, and copy-paste the failure(s) below, then iterate to green. Is the failure a flaky test unrelated to your change?

[github-actions[bot]]

:grey_exclamation: Gradle check result for d79340f2d1ae7381800244578ecc4d2d58cf5412: UNSTABLE

Please review all flaky tests that succeeded after retry and create an issue if one does not already exist to track the flaky failure.

[codecov[bot]]

Codecov Report

Attention: Patch coverage is 82.75862% with 20 lines in your changes missing coverage. Please review.

Project coverage is 71.77%. Comparing base (2fa8370) to head (d79340f). Report is 1 commits behind head on 2.x.

Files with missing lines	Patch %	Lines
...ava/org/opensearch/action/get/MultiGetRequest.java	33.33%	0 Missing and 2 partials :warning:
...search/client/indices/PutIndexTemplateRequest.java	0.00%	1 Missing :warning:
...search/index/rankeval/TransportRankEvalAction.java	50.00%	1 Missing :warning:
...n/indices/alias/TransportIndicesAliasesAction.java	50.00%	1 Missing :warning:
...ion/admin/indices/segments/PitSegmentsRequest.java	0.00%	1 Missing :warning:
...nsearch/action/admin/indices/stats/IndexStats.java	50.00%	1 Missing :warning:
.../indices/template/put/PutIndexTemplateRequest.java	0.00%	1 Missing :warning:
.../admin/indices/upgrade/get/IndexUpgradeStatus.java	0.00%	1 Missing :warning:
...ices/upgrade/get/TransportUpgradeStatusAction.java	0.00%	1 Missing :warning:
...min/indices/upgrade/get/UpgradeStatusResponse.java	0.00%	1 Missing :warning:
... and 9 more

Additional details and impacted files

```diff @@ Coverage Diff @@ ## 2.x #16563 +/- ## ============================================ - Coverage 71.95% 71.77% -0.18% + Complexity 65440 65385 -55 ============================================ Files 5312 5312 Lines 305033 305024 -9 Branches 44443 44443 ============================================ - Hits 219475 218931 -544 - Misses 67269 67881 +612 + Partials 18289 18212 -77 ```

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