fix: handle undefined bubble events (#9614)

Fixes #9610

Author: trueadm

.changeset/forty-comics-invent.md

@@ -0,0 +1,5 @@
+---
+'svelte': patch
+---
+
+fix: handle undefined bubble events

packages/svelte/src/internal/client/runtime.js

@@ -1530,7 +1530,7 @@ export function bubble_event($$props, event) {
 	const events = /** @type {Record<string, Function[] | Function>} */ (unwrap($$props).$$events)?.[
 		event.type
 	];
-	const callbacks = is_array(events) ? events.slice() : [events];
+	const callbacks = is_array(events) ? events.slice() : events == null ? [] : [events];
 	let fn;
 	for (fn of callbacks) {
 		// Preserve "this" context

packages/svelte/tests/runtime-legacy/samples/event-handler-undefined/_config.js

@@ -0,0 +1,14 @@
+import { flushSync } from 'svelte';
+import { test } from '../../test';
+
+export default test({
+	async test({ assert, target }) {
+		const input = target.querySelector('input');
+
+		flushSync(() => {
+			input?.click();
+		});
+
+		assert.htmlEqual(target.innerHTML, `<input>`);
+	}
+});

packages/svelte/tests/runtime-legacy/samples/event-handler-undefined/main.svelte

@@ -0,0 +1 @@
+<input on:click />