Setting defaultValue to null on DatePicker wrapped by Controller turns "isValid" to false

Describe the bug Using “defaultValue” = null on a DateField wrapped in Controller turns “isValid” in formState to “false”.

To Reproduce

1. Open attached CodeSandbox
2. Submit button is disabled because “isValid” is false
3. Change defaultValue={null} on second Field to defaultValue={new Date()} and Submit button is not disabled anymore when loading form again

Codesandbox link (Required) https://codesandbox.io/s/gallant-jang-cqm4d?file=/src/App.tsx

Expected behavior One should be able to initialize the field without a preset Date.

Additional context I can’t wrap my head around if this is an issue with the MUI DatePicker or with react-hook-form itself. Because the “date of birth” field in my CSB should be optional, it should also be initialized without a value. But even after entering a value, isValid stays false.

Maybe someone can have a look at my CSB example and figure out what I’m doing wrong, because I tried so much but can’t get it right somehow 😦

[MrBlue9]

Oh, now I see it! My ternary operators for both validations on that field are messed up! I got it working now! Thank you!

[MrBlue9]

Should “isValid” not be true and the form therefore submittable because the field “date of birth” is not required?