n8n 2.35.3 $json mutating Array methods return null

Minimal reproduction and version matrix for n8n issue #36540.

Confirmed behavior

Using official Docker images with isolated Edit Fields branches:

Expression	n8n 2.34.5	n8n 2.35.3
$json.data.sort()	array	null
$json.data.splice(0, 2)	removed items	null
$json.data.fill('X', 0, 2)	mutated array	null
$json.data.copyWithin(0, 2, 4)	mutated array	null
$json.data.reverse()	reversed array	reversed array
[...$json.data].sort()	sorted array	sorted array
$json.data.slice().sort()	sorted array	sorted array

The 2.35.3 copy-first variants for sort, splice, fill, and copyWithin were also verified and passed.

Environment

• n8nio/n8n:2.34.5 — Node.js v24.18.0
• n8nio/n8n:2.35.3 — Node.js v24.18.1
• n8n CLI execution
• default SQLite
• macOS + Docker Desktop on an arm64 host
• one independent input branch per expression to avoid cross-field mutation

Files

• workflow-isolated.json — authoritative version-comparison fixture
• workflow-workarounds.json — copy-first workaround fixture for 2.35.3
• workflow.json — initial combined-field control; not used as the authoritative matrix
• results/verification.json — normalized machine-readable results
• version-matrix.md — compact human-readable results

How to rerun

Use a disposable n8n environment for each target version, import workflow-isolated.json, and execute the workflow. Repeat with workflow-workarounds.json on 2.35.3. Keep the versions isolated so database/runtime state from one run cannot affect the other.

The n8n CLI currently expects an imported workflow ID for execute; the repository intentionally does not claim that the deprecated --file flag is a stable one-command runner.

Workaround

Copy the input array before calling a mutating method, for example:

{{ [...$json.data].sort() }}

The same copy-first pattern was verified for splice, fill, and copyWithin on 2.35.3.

The upstream reporter also observed that N8N_EXPRESSION_ENGINE=legacy makes the same expressions work again on 2.35.3. That engine-toggle result is upstream evidence; it is not part of the local XBSTACK verification matrix in this repository.

Evidence boundary

This repository confirms the observable regression between the two tested versions and the tested containment. It does not claim a specific internal root-cause commit unless n8n maintainers confirm one.

Full reproduction notes and production guidance: https://www.xbstack.com/en/ai/n8n-2353-json-array-methods-return-null/?utm_source=github&utm_medium=referral&utm_campaign=n8n_2353_array_null_regression&utm_content=repository_readme