I got thiserror when trying to access my menu which I created to access a customized res.partner model 

RPC_ERROR
Odoo Server Error
Traceback (most recent call last):
File "C:\Program Files\odoo-16\server\odoo\tools\cache.py", line 85, in lookup
r = d[key]
File "", line 2, in __getitem__
File "C:\Program Files\odoo-16\server\odoo\tools\func.py", line 87, in locked
return func(inst, *args, **kwargs)
File "C:\Program Files\odoo-16\server\odoo\tools\lru.py", line 34, in __getitem__
a = self.d[obj]
KeyError: ('res.partner', , (418, 'tree', None, 'fr_FR', res.company(1,), None))

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
File "C:\Program Files\odoo-16\server\odoo\http.py", line 1583, in _serve_db
return service_model.retrying(self._serve_ir_http, self.env)
File "C:\Program Files\odoo-16\server\odoo\service\model.py", line 134, in retrying
result = func()
File "C:\Program Files\odoo-16\server\odoo\http.py", line 1610, in _serve_ir_http
response = self.dispatcher.dispatch(rule.endpoint, args)
File "C:\Program Files\odoo-16\server\odoo\http.py", line 1807, in dispatch
result = self.request.registry['ir.http']._dispatch(endpoint)
File "C:\Program Files\odoo-16\server\odoo\addons\base\models\ir_http.py", line 154, in _dispatch
result = endpoint(**request.params)
File "C:\Program Files\odoo-16\server\odoo\http.py", line 696, in route_wrapper
result = endpoint(self, *args, **params_ok)
File "C:\Program Files\odoo-16\server\odoo\addons\web\controllers\dataset.py", line 42, in call_kw
return self._call_kw(model, method, args, kwargs)
File "C:\Program Files\odoo-16\server\odoo\addons\web\controllers\dataset.py", line 33, in _call_kw
return call_kw(request.env[model], method, args, kwargs)
File "C:\Program Files\odoo-16\server\odoo\api.py", line 457, in call_kw
result = _call_kw_model(method, model, args, kwargs)
File "C:\Program Files\odoo-16\server\odoo\api.py", line 430, in _call_kw_model
result = method(recs, *args, **kwargs)
File "C:\Program Files\odoo-16\server\odoo\addons\base\models\ir_ui_view.py", line 2494, in get_views
for [v_id, v_type] in views
File "C:\Program Files\odoo-16\server\odoo\addons\base\models\ir_ui_view.py", line 2494, in
for [v_id, v_type] in views
File "C:\Program Files\odoo-16\server\odoo\addons\base\models\ir_ui_view.py", line 2674, in get_view
result = dict(self._get_view_cache(view_id, view_type, **options))
File "", line 2, in _get_view_cache
File "C:\Program Files\odoo-16\server\odoo\tools\cache.py", line 90, in lookup
value = d[key] = self.method(*args, **kwargs)
File "C:\Program Files\odoo-16\server\odoo\addons\base\models\ir_ui_view.py", line 2634, in _get_view_cache
arch, view = self._get_view(view_id, view_type, **options)
File "C:\Program Files\odoo-16\server\odoo\addons\base\models\res_partner.py", line 428, in _get_view
arch, view = super()._get_view(view_id, view_type, **options)
File "C:\Program Files\odoo-16\server\odoo\addons\base\models\res_partner.py", line 103, in _get_view
arch, view = super()._get_view(view_id, view_type, **options)
File "C:\Program Files\odoo-16\server\odoo\addons\web\models\models.py", line 245, in _get_view
arch, view = super()._get_view(view_id, view_type, **options)
File "C:\Program Files\odoo-16\server\odoo\addons\base\models\ir_ui_view.py", line 2581, in _get_view
arch = view._get_combined_arch()
File "C:\Program Files\odoo-16\server\odoo\addons\base\models\ir_ui_view.py", line 999, in _get_combined_arch
arch = root.with_prefetch(tree_views._prefetch_ids)._combine(hierarchy)
File "C:\Program Files\odoo-16\server\odoo\addons\base\models\ir_ui_view.py", line 936, in _combine
arch = etree.fromstring(view.arch)
File "src\lxml\etree.pyx", line 3237, in lxml.etree.fromstring
File "src\lxml\parser.pxi", line 1896, in lxml.etree._parseMemoryDocument
File "src\lxml\parser.pxi", line 1777, in lxml.etree._parseDoc
File "src\lxml\parser.pxi", line 1082, in lxml.etree._BaseParser._parseUnicodeDoc
File "src\lxml\parser.pxi", line 615, in lxml.etree._ParserContext._handleParseResultDoc
File "src\lxml\parser.pxi", line 725, in lxml.etree._handleParseResult
File "src\lxml\parser.pxi", line 654, in lxml.etree._raiseParseError
File "", line 1
lxml.etree.XMLSyntaxError: Document is empty, line 1, column 1

The above server error caused the following client error:
RPC_ERROR: Odoo Server Error
at makeErrorFromResponse (http://localhost:8069/web/assets/213-d979079/web.assets_backend.min. js:970:163)
at XMLHttpRequest. (http://localhost:8069/web/assets/213-d979079/web.assets_backend.min.js :978:13)