contract/agreement/models/agreement_clause.py

from odoo import models, fields, api

#Main Agreement clause Records Model
class AgreementClause(models.Model):
     _name = 'partner_agreement.clause'
     _order = 'clause_sequence'

#General
     name = fields.Char(string="Title", required=True)
     clause_sequence = fields.Integer(string="Sequence")
     agreement = fields.Many2one('partner_agreement.agreement', string="Agreement", ondelete="cascade")
     section = fields.Many2one('partner_agreement.section', string="Section", ondelete="cascade")
     content = fields.Html(string="Clause Content")
     active = fields.Boolean(string="Active", default=True, help="If unchecked, it will allow you to hide the agreement without removing it.")

#Placeholder fields
     model_id = fields.Many2one('ir.model', string="Applies to", help="The type of document this template can be used with.")
     model_object_field = fields.Many2one('ir.model.fields', string="Field", help="Select target field from the related document model. If it is a relationship field you will be able to select a target field at the destination of the relationship.")
     sub_object = fields.Many2one('ir.model', string="Sub-model", help="When a relationship field is selected as first field, this field shows the document model the relationship goes to.")
     sub_model_object_field = fields.Many2one('ir.model.fields', string="Sub-field", help="When a relationship field is selected as first field, this field lets you select the target field within the destination document model (sub-model).")
     null_value = fields.Char(string="Default Value", help="Optional value to use if the target field is empty.")
     copyvalue = fields.Char(string="Placeholder Expression", help="Final placeholder expression, to be copy-pasted in the desired template field.")

     @api.model
     def create(self, vals):
        seq = self.env['ir.sequence'].next_by_code('agreement.clause') or '/'
        vals['clause_sequence'] = seq
        return super(AgreementClause, self).create(vals)