Slot drilling error when named slot is missing

[Jexordexan]

Version

3.0.0-alpha.7

Reproduction link

https://codesandbox.io/s/vue-3-slot-drilling-error-92srn

Steps to reproduce

Open the sandbox and check the console

What is expected?

Missing slots skip rendering.

What is actually happening?

Component throws an error and doesn't render any content

TypeError: Cannot read property 'name' of undefined
    at createSlots (https://unpkg.com/vue@3.0.0-alpha.7/dist/vue.global.js:9054:26)
    at Proxy.render (eval at compileToFunction (https://unpkg.com/vue@3.0.0-alpha.7/dist/vue.global.js:10172:24), <anonymous>:15:44)
    at renderComponentRoot (https://unpkg.com/vue@3.0.0-alpha.7/dist/vue.global.js:5056:55)
    at componentEffect (https://unpkg.com/vue@3.0.0-alpha.7/dist/vue.global.js:6891:55)
    at run (https://unpkg.com/vue@3.0.0-alpha.7/dist/vue.global.js:4060:22)
    at reactiveEffect (https://unpkg.com/vue@3.0.0-alpha.7/dist/vue.global.js:4041:18)
    at effect (https://unpkg.com/vue@3.0.0-alpha.7/dist/vue.global.js:4026:11)
    at setupRenderEffect (https://unpkg.com/vue@3.0.0-alpha.7/dist/vue.global.js:6889:29)
    at mountComponent (https://unpkg.com/vue@3.0.0-alpha.7/dist/vue.global.js:6882:11)
    at processComponent (https://unpkg.com/vue@3.0.0-alpha.7/dist/vue.global.js:6808:19)

---

I realize this might not be a common use case, but the practice of passing slot content to child components is useful for complex library components.

My use case is porting an autocomplete component from the v2 composition-api plugin to v3. One of the slots on the base component, Autocomplete, is named "suggestion", which, if it exists, is handed to the inner AutocompleteList component. It works fine with the v2 plugin but is broken in v3.

This bug also shows up if the fallback content is set for the named slot, which is strange because I would expect that fallback to create the necessary render function.

Offending Code:
https://github.com/vuejs/vue-next/blob/master/packages/runtime-core/src/helpers/createSlots.ts#L22