Fix crash when children are undefined (#1885)

* ensure children always exist

* update changelog

packages/@headlessui-vue/CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Call `displayValue` with a v-model of `ref(undefined)` on `ComboboxInput` ([#1865](https://github.com/tailwindlabs/headlessui/pull/1865))
 - Improve `Portal` detection for `Popover` components ([#1842](https://github.com/tailwindlabs/headlessui/pull/1842))
+- Fix crash when `children` are `undefined` ([#1885](https://github.com/tailwindlabs/headlessui/pull/1885))
 
 ## [1.7.2] - 2022-09-15
 

packages/@headlessui-vue/src/components/menu/menu.test.tsx

@@ -91,6 +91,12 @@ describe('Safe guards', () => {
 
 describe('Rendering', () => {
   describe('Menu', () => {
+    it('should not crash when rendering no children at all', () => {
+      renderTemplate(jsx`
+        <Menu></Menu>
+      `)
+    })
+
     it('should be possible to render a Menu using a default render prop', async () => {
       renderTemplate(jsx`
         <Menu v-slot="{ open }">

packages/@headlessui-vue/src/utils/render.ts

@@ -108,7 +108,7 @@ function _render({
   }
 
   if (as === 'template') {
-    children = flattenFragments(children as VNode[])
+    children = flattenFragments(children ?? [])
 
     if (Object.keys(incomingProps).length > 0 || Object.keys(attrs).length > 0) {
       let [firstChild, ...other] = children ?? []