feat: Better error when calling expression function on input that is undefined or null (#10009)

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');
+		});
+	});
 });