feat: Better error when calling expression function on input that is undefined or null

packages/nodes-base/nodes/Filter/V2/FilterV2.node.ts

@@ -6,6 +6,7 @@ import type {
 	INodeTypeBaseDescription,
 	INodeTypeDescription,
 } from 'n8n-workflow';
+import { ENABLE_LESS_STRICT_TYPE_VALIDATION } from '../../../utils/constants';
 
 export class FilterV2 implements INodeType {
 	description: INodeTypeDescription;
@@ -79,12 +80,8 @@ export class FilterV2 implements INodeType {
 						extractValue: true,
 					}) as boolean;
 				} catch (error) {
-					if (!options.looseTypeValidation) {
-						set(
-							error,
-							'description',
-							"Try changing the type of comparison. Alternatively you can enable 'Less Strict Type Validation' in the options.",
-						);
+					if (!options.looseTypeValidation && !error.description) {
+						set(error, 'description', ENABLE_LESS_STRICT_TYPE_VALIDATION);
 					}
 					set(error, 'context.itemIndex', itemIndex);
 					set(error, 'node', this.getNode());

packages/nodes-base/nodes/If/V2/IfV2.node.ts

@@ -6,6 +6,7 @@ import type {
 	INodeTypeBaseDescription,
 	INodeTypeDescription,
 } from 'n8n-workflow';
+import { ENABLE_LESS_STRICT_TYPE_VALIDATION } from '../../../utils/constants';
 
 export class IfV2 implements INodeType {
 	description: INodeTypeDescription;
@@ -79,12 +80,8 @@ export class IfV2 implements INodeType {
 						extractValue: true,
 					}) as boolean;
 				} catch (error) {
-					if (!options.looseTypeValidation) {
-						set(
-							error,
-							'description',
-							"Try changing the type of comparison. Alternatively you can enable 'Less Strict Type Validation' in the options.",
-						);
+					if (!options.looseTypeValidation && !error.description) {
+						set(error, 'description', ENABLE_LESS_STRICT_TYPE_VALIDATION);
 					}
 					set(error, 'context.itemIndex', itemIndex);
 					set(error, 'node', this.getNode());

packages/nodes-base/nodes/Switch/V3/SwitchV3.node.ts

@@ -12,6 +12,7 @@ import type {
 import { NodeConnectionType, NodeOperationError } from 'n8n-workflow';
 import set from 'lodash/set';
 import { capitalize } from '@utils/utilities';
+import { ENABLE_LESS_STRICT_TYPE_VALIDATION } from '../../../utils/constants';
 
 const configuredOutputs = (parameters: INodeParameters) => {
 	const mode = parameters.mode as string;
@@ -348,9 +349,8 @@ export class SwitchV3 implements INodeType {
 								},
 							) as boolean;
 						} catch (error) {
-							if (!options.looseTypeValidation) {
-								error.description =
-									"Try changing the type of comparison. Alternatively you can enable 'Less Strict Type Validation' in the options.";
+							if (!options.looseTypeValidation && !error.description) {
+								error.description = ENABLE_LESS_STRICT_TYPE_VALIDATION;
 							}
 							set(error, 'context.itemIndex', itemIndex);
 							set(error, 'node', this.getNode());

packages/nodes-base/utils/constants.ts

@@ -2,3 +2,6 @@ export const NODE_RAN_MULTIPLE_TIMES_WARNING =
 	"This node ran multiple times - once for each input item. You can change this by setting 'execute once' in the node settings. <a href='https://docs.n8n.io/flow-logic/looping/#executing-nodes-once' target='_blank'>More Info</a>";
 
 export const LOCALHOST = '127.0.0.1';
+
+export const ENABLE_LESS_STRICT_TYPE_VALIDATION =
+	"Try changing the type of comparison. Alternatively you can enable 'Less Strict Type Validation' in the options.";

packages/workflow/src/Extensions/ExpressionExtension.ts

@@ -17,6 +17,7 @@ import type { ExpressionChunk, ExpressionCode } from './ExpressionParser';
 import { joinExpression, splitExpression } from './ExpressionParser';
 import { booleanExtensions } from './BooleanExtensions';
 import type { ExtensionMap } from './Extensions';
+import { checkIfValueDefinedOrThrow } from './utils';
 
 const EXPRESSION_EXTENDER = 'extend';
 const EXPRESSION_EXTENDER_OPTIONAL = 'extendOptional';
@@ -514,6 +515,7 @@ export function extend(input: unknown, functionName: string, args: unknown[]) {
 	// any types have a function with that name. Then throw an error
 	// letting the user know the available types.
 	if (!foundFunction) {
+		checkIfValueDefinedOrThrow(input, functionName);
 		const haveFunction = EXTENSION_OBJECTS.filter((v) => functionName in v.functions);
 		if (!haveFunction.length) {
 			// This shouldn't really be possible but we should cover it anyway

packages/workflow/src/Extensions/utils.ts

@@ -1,4 +1,5 @@
 import { DateTime } from 'luxon';
+import { ExpressionExtensionError } from '../errors/expression-extension.error';
 
 // Utility functions and type guards for expression extensions
 
@@ -17,3 +18,15 @@ export const convertToDateTime = (value: string | Date | DateTime): DateTime | u
 	}
 	return converted;
 };
+
+export function checkIfValueDefinedOrThrow<T>(value: T, functionName: string): void {
+	if (value === undefined || value === null) {
+		throw new ExpressionExtensionError(
+			`${functionName}() could not be called on "${String(value)}" type`,
+			{
+				description:
+					'You are trying to access a field that does not exist, modify your expression or set a default value',
+			},
+		);
+	}
+}

packages/workflow/test/ExpressionExtensions/ExpressionExtension.test.ts

@@ -4,9 +4,10 @@
 
 /* eslint-disable n8n-local-rules/no-interpolation-in-regular-string */
 
-import { extendTransform } from '@/Extensions';
+import { extendTransform, extend } from '@/Extensions';
 import { joinExpression, splitExpression } from '@/Extensions/ExpressionParser';
 import { evaluate } from './Helpers';
+import { ExpressionExtensionError } from '../../src/errors/expression-extension.error';
 
 describe('Expression Extension Transforms', () => {
 	describe('extend() transform', () => {
@@ -242,4 +243,31 @@ describe('tmpl Expression Parser', () => {
 			expect(evaluate('={{ $ifEmpty({a: 1}, "default") }}')).toEqual({ a: 1 });
 		});
 	});
+
+	describe('Test extend with undefined', () => {
+		test('input is undefined', () => {
+			try {
+				extend(undefined, 'toDateTime', []);
+			} catch (error) {
+				expect(error).toBeInstanceOf(ExpressionExtensionError);
+				expect(error).toHaveProperty(
+					'message',
+					'toDateTime() could not be called on "undefined" type',
+				);
+			}
+		});
+		test('input is null', () => {
+			try {
+				extend(null, 'startsWith', []);
+			} catch (error) {
+				expect(error).toBeInstanceOf(ExpressionExtensionError);
+				expect(error).toHaveProperty('message', 'startsWith() could not be called on "null" type');
+			}
+		});
+		test('input should be converted to upper case', () => {
+			const result = extend('TEST', 'toUpperCase', []);
+
+			expect(result).toEqual('TEST');
+		});
+	});
 });