I am trying to migrate our custom_module to Odoo 15 code. This custom module works with DOM and has to read an xml file. But everytime I press on read file Iget this kind of error. On Odoo13 it worked fine but on 15 not anymore: 





Odoo Server Error

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/odoo/addons/base/models/ir_http.py", line 237, in _dispatch
    result = request.dispatch()
  File "/usr/lib/python3/dist-packages/odoo/http.py", line 687, in dispatch
    result = self._call_function(**self.params)
  File "/usr/lib/python3/dist-packages/odoo/http.py", line 359, 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 348, in checked_call
    result = self.endpoint(*a, **kw)
  File "/usr/lib/python3/dist-packages/odoo/http.py", line 916, in __call__
    return self.method(*args, **kw)
  File "/usr/lib/python3/dist-packages/odoo/http.py", line 535, in response_wrap
    response = f(*args, **kw)
  File "/usr/lib/python3/dist-packages/odoo/addons/web/controllers/main.py", line 1339, in call_button
    action = self._call_kw(model, method, args, kwargs)
  File "/usr/lib/python3/dist-packages/odoo/addons/web/controllers/main.py", line 1327, in _call_kw
    return call_kw(request.env[model], method, args, kwargs)
  File "/usr/lib/python3/dist-packages/odoo/api.py", line 464, in call_kw
    result = _call_kw_multi(method, model, args, kwargs)
  File "/usr/lib/python3/dist-packages/odoo/api.py", line 451, in _call_kw_multi
    result = method(recs, *args, **kwargs)
  File "/opt/Odoo/Custom_Addon/modul-x_invoice-master/models/x_invoice.py", line 599, in read_file
    self.name = self.get_file_name()
  File "/usr/lib/python3/dist-packages/odoo/fields.py", line 1217, in __set__
    records.write({self.name: write_value})
  File "/opt/Odoo/Custom_Addon/modul-x_invoice-master/models/x_invoice.py", line 654, in write
    self.write_file()
  File "/opt/Odoo/Custom_Addon/modul-x_invoice-master/models/x_invoice.py", line 606, in write_file
    self.set_xml_data()
  File "/opt/Odoo/Custom_Addon/modul-x_invoice-master/models/x_invoice.py", line 413, in set_xml_data
    self.domtree = self.get_xml_domtree()
Exception

The above exception was the direct cause of the following exception:

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/odoo/http.py", line 643, in _handle_exception
    return super(JsonRequest, self)._handle_exception(exception)
  File "/usr/lib/python3/dist-packages/odoo/http.py", line 301, in _handle_exception
    raise exception.with_traceback(None) from new_cause
AttributeError: 'x.invoice' object attribute 'domtree' is read-only