I want to add chatter to an appointment in odoo 12
i got this error 
ValueError: Field `message_follower_ids` does not exist
Error context:
View `Patient Form`
[view_id: 479, xml_id: my_clinic.patient_form, model: clinic.patient, parent_id: n/a]

model
class Appointment(models.Model):

    _name = 'clinic.appointment'
    _rec_name = 'date'
    _inherit = ['mail.thread']

    patient = fields.Many2one(comodel_name='clinic.patient', string='name')
    date = fields.Datetime(string='Appointment Date')
    office = fields.Many2one(
        comodel_name='clinic.office', string='office_name')
Views

    <record model="ir.ui.view" id="patient_form">
      <field name="name">Patient Form</field>
      <field name="model">clinic.patient</field>
      <field name="arch" type="xml">
        <form>
          <sheet>
            <group>
              <group>
                <field name="name"/>
                <field name="gender" />
              </group>
              <group>
                <field name="phone" widget='phone'/>
                <field name="email" widget='email' />
              </group>

            </group>
            <group>
              <tab>
                <field name="blood_group" />
              </tab>
            </group>
          </sheet>
          
          <div class="oe_chatter">
            <field name="message_follower_ids" widget="mail_followers"/>
            <field name="message_ids" widget="mail_thread"/>
          </div>
        </form>

      </field>
    </record>