computedAsync without initialState should return union T | undefined

[aphex]

Describe the bug

When using computedAsync in it's basic form:

const g = computedAsync(async () => {
  await new Promise((resolve) => setTimeout(resolve, 5000))

  return 'hello'
})

We get a type of const g: Ref<string>
It would be nice if we could get the type const g: Ref<string | undefined>

Without this the template assumes g will always be a string and TS has no issues.

For example something like this will throw a runtime error (Unhandled error during execution of render function ) but not be caught by typescript

<p>{{ g.charAt(1) }}</p>

Reproduction

https://stackblitz.com/edit/vitejs-vite-hmsvky

System Info

System:
  OS: Windows 11 10.0.22631
  CPU: (32) x64 Intel(R) Core(TM) i9-14900K
  Memory: 32.46 GB / 63.75 GB
Binaries:
  Node: 18.20.0 - ~\AppData\Local\pnpm\node.EXE
  npm: 10.5.0 - ~\AppData\Local\pnpm\npm.CMD
  pnpm: 8.15.7 - ~\AppData\Local\pnpm\pnpm.EXE
Browsers:
  Edge: Chromium (123.0.2420.97)
  Internet Explorer: 11.0.22621.1

Used Package Manager

pnpm

Validations

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• Read the Contributing Guidelines.
• Read the docs.
• Check that there isn't already an issue that reports the same bug to avoid creating a duplicate.
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• The provided reproduction is a minimal reproducible example of the bug.