How can I tell Formbit that the values are not null?

[TheFe91]

I'm developing a form with formbit in Typescript and I ran into this problem:

I have my initialValues defined in this way

const schema = yup.object().shape({
  adataord: yup.string().required(),
  dadataord: yup.string().required(),
  lbage: yup.string().required(),
  td_flags: yup.string().required(),
});

type FormValues = {
  adataord: string;
  dadataord: string;
  lbage: string;
  td_flags: string;
};

const initialValues: FormValues = {
  adataord: '',
  dadataord: '',
  lbage: '-1',
  td_flags: '99',
};

const { write, form } = useFormbit({ initialValues, yup: schema });

I have a useState defined in this way

const [filters, setFilters] = useState(initialValues);

At a certain point I want to do

const handleOnFilter = () => {
  setFilters({ ...form });
};

However this raises a typescript error, saying that string | undefined is not assignable to type string, obliging me to do

const handleOnFilter = () => {
    setFilters({
      adataord: form.adataord!,
      dadataord: form.dadataord!,
      lbage: form.lbage!,
      td_flags: form.td_flags!,
    });
  };

I'm not getting why formbit addresses the types as nullables, while I defined them as non-nullables.
Am I making any mistake?