Slot inside v-for not working

[edikdeisling]

Version

3.0.0-beta.16

Reproduction link

https://jsfiddle.net/Lcj5m6g4/

Steps to reproduce

1. Open jsfiddle
2. Click "inc" button
3. Watch console

What is expected?

No errors

What is actually happening?

TypeError: Cannot read property '0' of null

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This defect appeared in this vue version