Determine checkbox group inside array by appended object

[marilavoura]

On version 7.30.0 it has been added support for determining checkbox group based on defaultValues (#7938).
However, when the field that represents the checkbox group with only one checkbox is inside an array, that is empty in defaultValues, the solution provided is not working. Is there a way to also check appended values?

For example:
const { register, handleSubmit, control, watch } = useForm({ defaultValues: { array: [], } });
const { append } = useFieldArray({ name: "array", control });
append({ checkbox: [] })

The expected behavior was the checkbox to be unchecked, as the checkbox was initally seted as an empty array in append.

Here is a sandbox that reproduces the issue:
https://codesandbox.io/s/register-forked-tlflhj?file=/src/App.js