class DHACalendar(models.Model):
    _inherit = "resource.resource"

    calendar_id = fields.Many2one(
        "resource.calendar", string='Working Time',
        default=None,
        required=False,
        help="Define the schedule of resource")

    @api.model
    def default_get(self, fields):
        res = super(DHACalendar, self).default_get(fields)
        if not res.get('calendar_id') and res.get('company_id'):
            company = self.env['res.company'].browse(res['company_id'])
            res['calendar_id'] = None
        return res

    @api.model
    def create(self, values):
        values["calendar_id"] = False
        return super(DHACalendar, self).create(values)

    @api.onchange('company_id')
    def _onchange_company_id(self):
        if self.company_id:
            self.calendar_id = None

https://github.com/odoo/odoo/blob/11.0/addons/resource/models/resource.py#L655-L715

In odoo11alue - Resource, I want to not set default value. But it sets default.

How to Fix it?

Thanks.