When copying the old buffer value, if the old value is undefined (o…

[llsansun]

Re: #

Changelog

error：
TypeError: Cannot read properties of undefined (reading 'tileSize')
at TerrainBlock.update (terrain.ts:539:46)
at Terrain.update (terrain.ts:1752:29)
at component-scheduler.ts:299:35
at ReusableInvoker._invoke (component-scheduler.ts:251:13)
at ReusableInvoker.invoke (component-scheduler.ts:213:14)
at ComponentScheduler.updatePhase (component-scheduler.ts:504:28)
at Director.tick (director.ts:780:37)
at Game._updateCallback (game.ts:1086:22)
at Pacer.updateCallback [as _ccprivate$_callback] (pacer-web.js:4:1650)

*When terrain.rebuild(info) is called while the node is inactive, _layerBuffer is still an empty array []. When _rebuildLayerBuffer copies data from this empty array, undefined overwrites the pre‑initialized -1 values in the new buffer. Later, TerrainBlock.update() receives undefined as the layer ID. getLayer(undefined) returns undefined (not null), which bypasses the !== null check, eventually causing a crash when accessing undefined.tileSize.

Two fixes:

1. _rebuildLayerBuffer (root‑cause fix): When copying old buffer values, if the old value is undefined (out‑of‑bounds access on an empty array), preserve the default -1 instead of writing undefined.

2. getLayer (defensive fix): Return null when _layerList[id] is undefined, and filter cases where id === undefined. Ensure the caller’s !== null check works correctly for interception.

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Continuous Integration

This pull request:

• needs automatic test cases check.

  Manual trigger with @cocos-robot run test cases afterward.

• does not change any runtime related code or build configuration

  If any reviewer thinks the CI checks are needed, please uncheck this option, then close and reopen the issue.

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Compatibility Check

This pull request:

• changes public API, and have ensured backward compatibility with deprecated features.
• affects platform compatibility, e.g. system version, browser version, platform sdk version, platform toolchain, language version, hardware compatibility etc.
• affects file structure of the build package or build configuration which requires user project upgrade.
• introduces breaking changes, please list all changes, affected features and the scope of violation.

[github-actions]

Code Size Check Report

Wechat (WASM)	Before	After	Diff
2D Empty (legacy pipeline)	1015436 bytes	1015436 bytes	✅ 0 bytes
2D All (legacy pipeline)	2683579 bytes	2683579 bytes	✅ 0 bytes
2D All (new pipeline)	2775832 bytes	2775832 bytes	✅ 0 bytes
(2D + 3D) All	10033405 bytes	10033446 bytes	⚠️ +41 bytes

Web (WASM + ASMJS)	Before	After	Diff
(2D + 3D) All	16869823 bytes	16869864 bytes	⚠️ +41 bytes

Interface Check Report

This pull request does not change any public interfaces !

[star-e]

polyfill of ?? will increase code size a bit.

The following code might have smaller size.

const v = this._layerList[id];
return v !== undefined ? v | null;

[star-e]

@cocos-robot run test cases

[github-actions]

@llsansun, Please check the result of run test cases:

• Test Platform: PR-Test
• Editor Version: v4.0.0
• Task Result: FAIL
• Task URL: https://cctest.cocos.org/#/reportview/PR-TEST/d52ed475-1f8a-4b62-9764-03764631ff4b/-1
• GitHub Action: https://github.com/cocos/cocos4/actions/runs/33615935827

Task Details

Platform	build	boot	runned	crashScene	FailScene
web-mobile	PASS	PASS	FAIL		frame-anim
ios	PASS	PASS	PASS
mac	PASS	PASS	PASS

[github-actions]

@llsansun, Please check the result of run test cases:

• Test Platform: PR-Test
• Editor Version: v4.0.0
• Task Result: PASS
• Task URL: https://cctest.cocos.org/#/reportview/PR-TEST/659488c2-d5d6-4c3b-aa46-95e2948203a6/-1
• GitHub Action: https://github.com/cocos/cocos4/actions/runs/33615935827

Task Details