Hello everyone

I've created a custom selection field called payment_status which is not stored. I want to create filter for this without storing it. for this I've added the search function. my code is:

 payment_status = fields.Selection(        [            ("not_paid", "Not Paid"),            ("partially_paid", "Partially Paid"),            ("fully_paid", "Fully Paid"),        ],        compute="_computepaid", search="_search_payment_status"    )

 def _search_payment_status(self,operator, value):
	​if value not in ['not_paid', 'partially_paid', 'fully_paid']:
	​	​return [('id', 'in', [])]        
	​search_domain = [('payment_status', '=', value)]        
	​for rec in self:            
	​	​orders = rec.env['purchase.order'].search(search_domain)            
	​	​return [('id', 'in', orders.ids)]

but this is generating the following error:

Odoo Server Error
Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/odoo/http.py", line 624, in _handle_exception
    return super(JsonRequest, self)._handle_exception(exception)
  File "/usr/lib/python3/dist-packages/odoo/http.py", line 310, in _handle_exception
    raise pycompat.reraise(type(exception), exception, sys.exc_info()[2])
  File "/usr/lib/python3/dist-packages/odoo/tools/pycompat.py", line 14, in reraise
    raise value
  File "/usr/lib/python3/dist-packages/odoo/http.py", line 669, in dispatch
    result = self._call_function(**self.params)
  File "/usr/lib/python3/dist-packages/odoo/http.py", line 350, in _call_function
    return checked_call(self.db, *args, **kwargs)
  File "/usr/lib/python3/dist-packages/odoo/service/model.py", line 94, in wrapper
    return f(dbname, *args, **kwargs)
  File "/usr/lib/python3/dist-packages/odoo/http.py", line 339, in checked_call
    result = self.endpoint(*a, **kw)
  File "/usr/lib/python3/dist-packages/odoo/http.py", line 915, in __call__
    return self.method(*args, **kw)
  File "/usr/lib/python3/dist-packages/odoo/http.py", line 515, in response_wrap
    response = f(*args, **kw)
  File "/usr/lib/python3/dist-packages/odoo/addons/web/controllers/main.py", line 1300, in search_read
    return self.do_search_read(model, fields, offset, limit, domain, sort)
  File "/usr/lib/python3/dist-packages/odoo/addons/web/controllers/main.py", line 1319, in do_search_read
    return Model.web_search_read(domain, fields, offset=offset, limit=limit, order=sort)
  File "/usr/lib/python3/dist-packages/odoo/addons/web/models/models.py", line 48, in web_search_read
    records = self.search_read(domain, fields, offset=offset, limit=limit, order=order)
  File "/usr/lib/python3/dist-packages/odoo/models.py", line 4964, in search_read
    records = self.search(domain or [], offset=offset, limit=limit, order=order)
  File "/usr/lib/python3/dist-packages/odoo/models.py", line 1655, in search
    res = self._search(args, offset=offset, limit=limit, order=order, count=count)
  File "/usr/lib/python3/dist-packages/odoo/models.py", line 4506, in _search
    query = self._where_calc(args)
  File "/usr/lib/python3/dist-packages/odoo/models.py", line 4226, in _where_calc
    e = expression.expression(domain, self)
  File "/usr/lib/python3/dist-packages/odoo/osv/expression.py", line 681, in __init__
    self.parse()
  File "/usr/lib/python3/dist-packages/odoo/osv/expression.py", line 948, in parse
    model._flush_search(domain, order='id')
  File "/usr/lib/python3/dist-packages/odoo/models.py", line 4422, in _flush_search
    domain = list(domain) + (self.env['ir.rule']._compute_domain(self._name, 'read') or [])
TypeError: 'NoneType' object is not iterable

I even tried to add conditions for None records but it doesn't work.
Can anyone please help me on this?