I have inherited the res.partner form and python, and made some mods. When using the following two fields for calculating an age/birth year, they work perfectly in the main form view.

When I open the form view from an embedded kanban view, I get the error below. It's the same form! Can anyone help me get rid of the error please?

UncaughtPromiseError > TypeError

Uncaught Promise > value.toFixed is not a function

birth_year = fields.Integer(string='Birth Year')
age = fields.Integer(string='Age', compute='_compute_age', inverse='_inverse_compute_age')

@api.onchange('age')
def _inverse_compute_age(self):
    for record in self:
        if record.age:
            age = record.age
            today = date.today()
            birthYear = today - relativedelta.relativedelta(years=age)
            record.birth_year = birthYear.year

@api.onchange('birth_year')
def _compute_age(self):
    for record in self:
        if record.birth_year:
            birthYear = record.birth_year
            thisYear = date.today().year
            age = thisYear - birthYear
            record.age = age