fix(core): Fix task runner validation error on array of arrays (#15106)

packages/@n8n/task-runner/src/js-task-runner/__tests__/result-validation.test.ts

@@ -1,5 +1,6 @@
 import { ValidationError } from '@/js-task-runner/errors/validation-error';
 import {
+	NonArrayOfObjectsError,
 	validateRunForAllItemsOutput,
 	validateRunForEachItemOutput,
 } from '@/js-task-runner/result-validation';
@@ -24,6 +25,13 @@ describe('result validation', () => {
 			}).not.toThrow();
 		});
 
+		it('should throw a NonArrayOfObjectsError if the output is an array of arrays (empty)', () => {
+			expect(() => {
+				// @ts-expect-error Intentionally invalid
+				validateRunForAllItemsOutput([[]]);
+			}).toThrowError(NonArrayOfObjectsError);
+		});
+
 		test.each([
 			['binary', {}],
 			['pairedItem', {}],

packages/@n8n/task-runner/src/js-task-runner/obj-utils.ts

@@ -1,4 +1,4 @@
-export function isObject(maybe: unknown): maybe is { [key: string]: unknown } {
+export function isObject(maybe: unknown): maybe is object {
 	return (
 		typeof maybe === 'object' && maybe !== null && !Array.isArray(maybe) && !(maybe instanceof Date)
 	);

packages/@n8n/task-runner/src/js-task-runner/result-validation.ts

@@ -50,20 +50,26 @@ function validateItem({ json, binary }: INodeExecutionData, itemIndex: number) {
 	}
 }
 
+export class NonArrayOfObjectsError extends ValidationError {
+	constructor() {
+		super({
+			message: "Code doesn't return items properly",
+			description: 'Please return an array of objects, one for each item you would like to output.',
+		});
+	}
+}
+
 /**
  * Validates the output of a code node in 'Run for All Items' mode.
  */
 export function validateRunForAllItemsOutput(
 	executionResult: INodeExecutionData | INodeExecutionData[] | undefined,
 ) {
-	if (typeof executionResult !== 'object') {
-		throw new ValidationError({
-			message: "Code doesn't return items properly",
-			description: 'Please return an array of objects, one for each item you would like to output.',
-		});
-	}
-
 	if (Array.isArray(executionResult)) {
+		for (const item of executionResult) {
+			if (!isObject(item)) throw new NonArrayOfObjectsError();
+		}
+
 		/**
 		 * If at least one top-level key is an n8n item key (`json`, `binary`, etc.),
 		 * then require all item keys to be an n8n item key.
@@ -81,6 +87,8 @@ export function validateRunForAllItemsOutput(
 				validateTopLevelKeys(item, index);
 			}
 		}
+	} else if (!isObject(executionResult)) {
+		throw new NonArrayOfObjectsError();
 	}
 
 	const returnData = normalizeItems(executionResult);