AttributeError: 'NoneType' object has no attribute 'get_style_context'

Versions

• OS: Debian GNU/Linux bullseye/sid
• GTK Version: 3.24.23
• PyGObject Version: 3.38.0
• GLib Version : 2.66.2
• python-nbxmpp Version: 2.0.2
• Gajim Version: 1.3.1

Traceback

Traceback (most recent call last):
  File "/usr/lib/python3/dist-packages/gajim/app_actions.py", line 175, in on_server_info
    open_window('ServerInfo', account=account)
  File "/usr/lib/python3/dist-packages/gajim/gtk/util.py", line 823, in open_window
    window = window_cls(**kwargs)
  File "/usr/lib/python3/dist-packages/gajim/gtk/server_info.py", line 76, in __init__
    self._add_connection_info()
  File "/usr/lib/python3/dist-packages/gajim/gtk/server_info.py", line 99, in _add_connection_info
    self._ui.conection_type.get_style_context().add_class('error-color')
AttributeError: 'NoneType' object has no attribute 'get_style_context'

Steps to reproduce the problem

Accounts → account → Server Info