chore(core): Allow undefined in the node output value (#18198)

package.json

@@ -37,7 +37,7 @@
     "optimize-svg": "find ./packages -name '*.svg' ! -name 'pipedrive.svg' -print0 | xargs -0 -P16 -L20 npx svgo",
     "setup-backend-module": "node scripts/ensure-zx.mjs && zx scripts/backend-module/setup.mjs",
     "start": "run-script-os",
-    "start:default": "cd packages/cli/bin && ./n8n",
+    "start:default": "cd packages/cli/bin && node --inspect ./n8n",
     "start:tunnel": "./packages/cli/bin/n8n start --tunnel",
     "start:windows": "cd packages/cli/bin && n8n",
     "test": "JEST_JUNIT_CLASSNAME={filepath} turbo run test",

packages/core/src/utils/__tests__/is-json-compatible.test.ts

@@ -99,12 +99,6 @@ describe('isJsonCompatible', () => {
 			errorPath: 'value.nan',
 			errorMessage: 'is NaN, which is not JSON-compatible',
 		},
-		{
-			name: 'undefined',
-			value: { undefined },
-			errorPath: 'value.undefined',
-			errorMessage: 'is of unknown type (undefined) with value undefined',
-		},
 		{
 			name: 'an object with symbol keys',
 			value: { [Symbol.for('key')]: 1 },
@@ -125,6 +119,7 @@ describe('isJsonCompatible', () => {
 	const objectRef = {};
 	test.each([
 		{ name: 'null', value: { null: null } },
+		{ name: 'undefined', value: { noValue: undefined } },
 		{ name: 'an array of primitives', value: { array: [1, 'string', true, false] } },
 		{
 			name: 'an object without a prototype chain',

packages/core/src/utils/is-json-compatible.ts

@@ -1,3 +1,4 @@
+// eslint-disable-next-line complexity
 const check = (
 	val: unknown,
 	path = 'value',
@@ -6,7 +7,7 @@ const check = (
 ): { isValid: true } | { isValid: false; errorPath: string; errorMessage: string } => {
 	const type = typeof val;
 
-	if (val === null || type === 'boolean' || type === 'string') {
+	if (val === null || type === 'boolean' || type === 'string' || type === 'undefined') {
 		return { isValid: true };
 	}
 
@@ -46,7 +47,6 @@ const check = (
 		return { isValid: true };
 	}
 
-	if (type === 'object') {
 	if (stack.has(val)) {
 		return {
 			isValid: false,
@@ -85,13 +85,6 @@ const check = (
 	}
 	stack.delete(val);
 	return { isValid: true };
-	}
-
-	return {
-		isValid: false,
-		errorPath: path,
-		errorMessage: `is of unknown type (${type}) with value ${JSON.stringify(val)}`,
-	};
 };
 
 /**