How to use put an 'empty' value in react-hook-forms defaultValues with Typescript?

I use react-hook-forms with typescript and react native. When I set the defaultValues field in the useForm method I need to have in the beginning empty fields, there is no problem when the field is a string, but I have fields that for example should be a date. When I set the date to undefined I get a warning - fieldname is missing in the 'defaultValue' prop of either its controller or useForm, and when I try to set it to null I get some TypeScript error that the field in defaultValues must be either a Date or undefined, since react-hook-formsDefaultValues type can accept each field as an actual value or undefined.

So basically for each solution I get an error / warning. How can I solve that?

Thanks ahead.