Server-side rendering a component with conditional slot causes error

[Andersso]

Environment

Nuxi 3.0.0-rc.10 RootDir: /sandbox Nuxt project info:

---

• Operating System: Linux
• Node Version: v14.19.3
• Nuxt Version: 3.0.0-rc.10
• Nitro Version: 0.5.3
• Package Manager: [email protected]
• Builder: vite
• User Config: -
• Runtime Modules: -
• Build Modules: -

---

Reproduction

https://codesandbox.io/s/dawn-morning-b454k7?file=/pages/index.vue

Juicy bit: <FooComponent> <template v-if="true" #first> Hello conditional </template> </FooComponent>

Describe the bug

• When rendering a component slot with a condition that evaluates to true, an error will be thrown, the slot is however rendered correctly.
• It only seems to happen during SSR.
• Conditions that evaluates to false does not throw an error

Additional context

In RC 8 this was working fine

Logs

[nitro] [dev] [unhandledRejection] TypeError: Cannot set property 'key' of undefined
    at slots.<computed> (/sandbox/node_modules/@vue/runtime-core/dist/runtime-core.cjs.js:2924:29)
    at ssrRenderSlotInner (/sandbox/node_modules/@vue/server-renderer/dist/server-renderer.cjs.js:628:21)
    at Module.ssrRenderSlot (/sandbox/node_modules/@vue/server-renderer/dist/server-renderer.cjs.js:618:5)
    at _sfc_ssrRender (/sandbox/components/FooComponent.vue:7:25)
    at renderComponentSubTree (/sandbox/node_modules/@vue/server-renderer/dist/server-renderer.cjs.js:254:17)
    at renderComponentVNode (/sandbox/node_modules/@vue/server-renderer/dist/server-renderer.cjs.js:188:16)
    at Module.ssrRenderComponent (/sandbox/node_modules/@vue/server-renderer/dist/server-renderer.cjs.js:612:12)
    at _sfc_ssrRender (/sandbox/pages/index.vue:60:31)
    at renderComponentSubTree (/sandbox/node_modules/@vue/server-renderer/dist/server-renderer.cjs.js:254:17)
    at renderComponentVNode (/sandbox/node_modules/@vue/server-renderer/dist/server-renderer.cjs.js:188:16)

[danielroe]

You can track in https://github.com/vuejs/core/issues/6651.