Exception when invoicing multiple sale orders

[TelmoSuarez]

Module

account_payment_sale

Describe the bug

When trying to invoice 2 or more sale orders and some having payment mode and others having it blank throws python exception.

Traceback (most recent call last):
File "/opt/odoo/odoo/http.py", line 1632, in _serve_db
return service_model.retrying(self._serve_ir_http, self.env)
File "/opt/odoo/odoo/service/model.py", line 133, in retrying
result = func()
File "/opt/odoo/odoo/http.py", line 1659, in _serve_ir_http
response = self.dispatcher.dispatch(rule.endpoint, args)
File "/opt/odoo/odoo/http.py", line 1863, in dispatch
result = self.request.registry['ir.http']._dispatch(endpoint)
File "/opt/odoo/odoo/addons/base/models/ir_http.py", line 154, in _dispatch
result = endpoint(**request.params)
File "/opt/odoo/odoo/http.py", line 716, in route_wrapper
result = endpoint(self, *args, **params_ok)
File "/opt/odoo/addons/web/controllers/dataset.py", line 46, in call_button
action = self._call_kw(model, method, args, kwargs)
File "/opt/odoo/addons/web/controllers/dataset.py", line 33, in _call_kw
return call_kw(request.env[model], method, args, kwargs)
File "/opt/odoo/odoo/api.py", line 468, in call_kw
result = _call_kw_multi(method, model, args, kwargs)
File "/opt/odoo/odoo/api.py", line 453, in _call_kw_multi
result = method(recs, *args, **kwargs)
File "/opt/odoo/addons/sale/wizard/sale_make_invoice_advance.py", line 149, in create_invoices
self._create_invoices(self.sale_order_ids)
File "/opt/odoo/addons/sale/wizard/sale_make_invoice_advance.py", line 161, in _create_invoices
return sale_orders._create_invoices(final=self.deduct_down_payments)
File "/opt/odoo/addons/sale/models/sale_order.py", line 1149, in _create_invoices
invoice_vals_list = sorted(
TypeError: '<' not supported between instances of 'NoneType' and 'int'

The above server error caused the following client error:
RPC_ERROR: Odoo Server Error
RPC_ERROR
at makeErrorFromResponse (http://oca-bank-payment-16-0-b6a3937ce8b9.runboat.odoo-community.org/web/assets/448-1b8fd59/web.assets_backend.min.js:997:163)
at XMLHttpRequest. (http://oca-bank-payment-16-0-b6a3937ce8b9.runboat.odoo-community.org/web/assets/448-1b8fd59/web.assets_backend.min.js:1005:13)

To Reproduce

Affected versions:16.0

Steps to reproduce the behavior:

1. Install account_payment_sale
2. Create 2 sales.
3. Establish payment mode in one order and leave it blank in the other.
4. Invoice both sales.

Expected behavior
Generates invoices and doesn't throw exception.