[PIT finder] return empty generator if first page is empty

[pgayvallet]

Summary

Makes the PIT finder more consistent by ignoring empty first page and not yielding it (as this is also what is done for other pages)

[pgayvallet]

@elasticmachine merge upstream

[pgayvallet]

@elasticmachine merge upstream

[pgayvallet]

Even if this is an edge case, it is possible to specify aggregations with a PIT search, and this is effectively done at least once in our code:

kibana/x-pack/plugins/fleet/server/services/security/uninstall_token_service/index.ts

Lines 266 to 276 in 0ae3b23

	let aggResults: UninstallTokenSOAggregationBucket[] = [];
	for await (const result of idFinder.find()) {
	if (
	!result?.aggregations?.by_policy_id.buckets ||
	!Array.isArray(result?.aggregations?.by_policy_id.buckets)
	) {
	break;
	}
	aggResults = result.aggregations.by_policy_id.buckets;
	break;
	}

Note that this specific usage could be adapted (given there isn't any reason to use a PIT search here), but we scenario remains valid more globally, so we still have to check for aggregations and yield, otherwise there's no way for the API consumers to retrieve their aggregation results in case of empty hits.

[pgayvallet]

cc @elastic/fleet as you may want to adapt this snippet to use a standard SOR.find call instead of a PIT given you break on first page.

[kibana-ci]

💚 Build Succeeded

• Buildkite Build
• Commit: e3e2b14

Metrics [docs]

✅ unchanged

History

• 💚 Build #178841 succeeded d9ee81e
• 💔 Build #178719 failed 6d48e10
• 💔 Build #177992 failed 47cceaa
• 💔 Build #177820 failed 7040c65
• 💔 Build #177439 failed 5e47e7a
• 💔 Build #177178 failed 5b8fc73

To update your PR or re-run it, just comment with:
@elasticmachine merge upstream

[elasticmachine]

Pinging @elastic/kibana-core (Team:Core)

[jloleysens]

LGTM!