Computed map.get with key `undefined` is not reactive

[inctec-leo]

Vue version

@aa9ef23

Link to minimal reproduction

https://play.vuejs.org/#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

Steps to reproduce

• Run the linked SFC playground
• computed Map key test will be updated
• computed Map key undefined not

What is expected?

computed(() => map.get(undefined)) should be reactive

What is actually happening?

computed(() => map.get(undefined)) doesn't update if map.set(undefined) is called

System Info

No response

Any additional comments?

No response