i declared two field 'firstname' and 'secondname' in the rh.employee model and i want to concatenate both of them on the name field.

here is the function that i am declared 

def create(self, cr, uid, vals, context=None):

        new_id = super(HrEmployeePrivate, self).create(cr, uid, vals, context=context)

        names = (vals['Prénom'], vals['Nom'])

        fullname = " ".join([s for s in names if s])

        vals['name'] = fullname

        return new_id

and i call the function in the field name as well 

name = fields.Char(string="Employee Name",compute='create', related='resource_id.name', store=True, readonly=False, tracking=True)

but when i clck save, i get

the operation cannot be completed,

probably due to the following: 

creation/update: a mandatory field is not correctly set