Bug when stubbing async components

[ymhr]

Version

1.0.0-beta.25

Reproduction link

https://github.com/ymhr/vue-test-utils-stub-async-component-bug

Steps to reproduce

Test a component which imports an async component, and try and stub the async component.

What is expected?

It should render the component with your stub in place of the async component.

What is actually happening?

It errors with TypeError: Cannot read property 'attrs' of undefined

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This may be related to #1012, but that does seem like a different issue.
This does not appear to have been an error in beta.20.