I was working with Yup but now I have to use Joi for data validation.

I would like to do the equivalent of this Yup with Joi :

Yup.boolean().nullable().transform((value) => (value === null ? false : value));

I tried many things but none worked :

Joi.boolean().allow(null).custom((value, helper) => {
                if (value === null) {
                    return false;
                }

                return value;
            });

Joi.boolean().allow(null).cast("string").custom((value, helper) => {
                if (value === "null") {
                    return false;
                }

                return value;
            });

Joi.boolean().allow(null).cast("string").falsy("null")