CODE EXAMPLE FOR JAVASCRIPT

how to make a field not required with joi

let schema = {};

  let stations = {
    contact: {
      first_name: Joi.string().min(2).max(10).regex(Regex.alphabeta, 'alphabeta').allow("").error(JoiCustomErrors),
      last_name: Joi.string().min(2).max(10).regex(Regex.alphabeta, 'alphabeta').allow("").error(JoiCustomErrors),
      phone: Joi.string().min(10).max(10).regex(Regex.num, 'num').allow("").error(JoiCustomErrors),
    },
    address: {
      place: Joi.string().min(2).max(10).regex(Regex.alphanum, 'alphanum').required().error(JoiCustomErrors),
      city: Joi.string().min(2).max(30).required().error(JoiCustomErrors),
      street: Joi.string().min(2).max(30).regex(Regex.alphabeta, 'alphabeta').required().error(JoiCustomErrors),
      house_number: Joi.string().min(1).max(6).regex(Regex.alphanum, 'alphanum').allow("").error(JoiCustomErrors)
    },
    passengers_amount: Joi.number().min(0).max(4).required().error(JoiCustomErrors),
    notes: Joi.string().min(2).max(100).regex(Regex.alphanum, 'alphanum').allow("").error(JoiCustomErrors)
  };
  schema.stations = Joi.array().items(stations).min(1).max(5).required().error(JoiCustomErrors);