Traceback (most recent call last):
  File "/odoo/odoo-server/odoo/addons/base/models/ir_http.py", line 237, in _dispatch
    result = request.dispatch()
  File "/odoo/odoo-server/odoo/http.py", line 687, in dispatch
    result = self._call_function(**self.params)
  File "/odoo/odoo-server/odoo/http.py", line 359, in _call_function
    return checked_call(self.db, *args, **kwargs)
  File "/odoo/odoo-server/odoo/service/model.py", line 94, in wrapper
    return f(dbname, *args, **kwargs)
  File "/odoo/odoo-server/odoo/http.py", line 348, in checked_call
    result = self.endpoint(*a, **kw)
  File "/odoo/odoo-server/odoo/http.py", line 916, in __call__
    return self.method(*args, **kw)
  File "/odoo/odoo-server/odoo/http.py", line 535, in response_wrap
    response = f(*args, **kw)
  File "/odoo/odoo-server/addons/web/controllers/main.py", line 1351, in call_button
    action = self._call_kw(model, method, args, kwargs)
  File "/odoo/odoo-server/addons/web/controllers/main.py", line 1339, in _call_kw
    return call_kw(request.env[model], method, args, kwargs)
  File "/odoo/odoo-server/odoo/api.py", line 464, in call_kw
    result = _call_kw_multi(method, model, args, kwargs)
  File "/odoo/odoo-server/odoo/api.py", line 451, in _call_kw_multi
    result = method(recs, *args, **kwargs)
  File "", line 2, in button_immediate_upgrade
  File "/odoo/odoo-server/odoo/addons/base/models/ir_module.py", line 74, in check_and_log
    return method(self, *args, **kwargs)
  File "/odoo/odoo-server/odoo/addons/base/models/ir_module.py", line 662, in button_immediate_upgrade
    return self._button_immediate_function(type(self).button_upgrade)
  File "/odoo/odoo-server/odoo/addons/base/models/ir_module.py", line 600, in _button_immediate_function
    registry = modules.registry.Registry.new(self._cr.dbname, update_module=True)
  File "/odoo/odoo-server/odoo/modules/registry.py", line 87, in new
    odoo.modules.load_modules(registry, force_demo, status, update_module)
  File "/odoo/odoo-server/odoo/modules/loading.py", line 513, in load_modules
    env['ir.model.data']._process_end(processed_modules)
  File "/odoo/odoo-server/odoo/addons/base/models/ir_model.py", line 2269, in _process_end
    self._process_end_unlink_record(record)
  File "/odoo/odoo-server/addons/website/models/ir_model_data.py", line 36, in _process_end_unlink_record
    return super()._process_end_unlink_record(record)
  File "/odoo/odoo-server/odoo/addons/base/models/ir_model.py", line 2198, in _process_end_unlink_record
    record.unlink()
  File "/odoo/odoo-server/odoo/addons/base/models/ir_model.py", line 1375, in unlink
    self._process_ondelete()
  File "/odoo/odoo-server/odoo/addons/base/models/ir_model.py", line 1423, in _process_ondelete
    ondelete = (field.ondelete or {}).get(selection.value)
Exception

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

Traceback (most recent call last):
  File "/odoo/odoo-server/odoo/http.py", line 643, in _handle_exception
    return super(JsonRequest, self)._handle_exception(exception)
  File "/odoo/odoo-server/odoo/http.py", line 301, in _handle_exception
    raise exception.with_traceback(None) from new_cause
AttributeError: 'Char' object has no attribute 'ondelete'