when does not work with number

I get error: TypeError: Cannot read property 'length' of undefined

For example I have this validation:

const agreementDurationAmount = Yup.number().when('agreementDuration', (agreementDuration) => {
  if(agreementDuration === 'Miesięczny') {
    return Yup.number().min(1, 'Czas trwania umowy: wprowadź liczbę miesięcy');
  }
  if(agreementDuration === 'Tygodniowy') {
    return Yup.number().min(1, 'Czas trwania umowy: wprowadź liczbę tygodni');
  }
  return Yup.number();
});

And such object:

{
  agreementDuration: 'Nieokreślony',
  agreementDurationAmount: 0,
}

[liltechnomancer]

If anyones reading this. If you use when in a schema the field it depends on should also be in the schema. So @wieseljonas would need to declare a type and rules for mainType in the same schema as landSurface.

[rofrol]

Works, I just needed to add:

agreementPenaltyEnable: yup.boolean(),

Like this:

export const uodValidation = yup.object().shape({
  agreementPenaltyEnable: yup.boolean(),
  agreementPenalty,
});