Fatbuildrweb fails on keyring.asc HTTP request when keyring does not exist

[rezib]

For example:

uwsgi[62808]: uWSGIWorker4Core0: [ERROR] Exception on /devs/keyring.asc [GET]
uwsgi[62808]: Traceback (most recent call last):
uwsgi[62808]:   File "/usr/lib/python3/dist-packages/flask/app.py", line 2525, in wsgi_app
uwsgi[62808]:     response = self.full_dispatch_request()
uwsgi[62808]:                ^^^^^^^^^^^^^^^^^^^^^^^^^^^^
uwsgi[62808]:   File "/usr/lib/python3/dist-packages/flask/app.py", line 1822, in full_dispatch_request
uwsgi[62808]:     rv = self.handle_user_exception(e)
uwsgi[62808]:          ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
uwsgi[62808]:   File "/usr/lib/python3/dist-packages/flask/app.py", line 1820, in full_dispatch_request
uwsgi[62808]:     rv = self.dispatch_request()
uwsgi[62808]:          ^^^^^^^^^^^^^^^^^^^^^^^
uwsgi[62808]:   File "/usr/lib/python3/dist-packages/flask/app.py", line 1796, in dispatch_request
uwsgi[62808]:     return self.ensure_sync(self.view_functions[rule.endpoint])(**view_args)
uwsgi[62808]:            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
uwsgi[62808]:   File "/usr/lib/python3/dist-packages/fatbuildr/protocols/http/server/views.py", line 145, in wrapped
uwsgi[62808]:     return view(instance, *args, **kwargs)
uwsgi[62808]:            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
uwsgi[62808]:   File "/usr/lib/python3/dist-packages/fatbuildr/protocols/http/server/views.py", line 576, in keyring
uwsgi[62808]:     mem.write(connection.keyring_export().encode())
uwsgi[62808]:               ^^^^^^^^^^^^^^^^^^^^^^^^^^^
uwsgi[62808]:   File "/usr/lib/python3/dist-packages/fatbuildr/protocols/dbus/client.py", line 58, in error_handler_wrapper
uwsgi[62808]:     return method(*args, **kwargs)
uwsgi[62808]:            ^^^^^^^^^^^^^^^^^^^^^^^
uwsgi[62808]:   File "/usr/lib/python3/dist-packages/fatbuildr/protocols/dbus/client.py", line 306, in keyring_export
uwsgi[62808]:     return self.proxy.KeyringExport
uwsgi[62808]:            ^^^^^^^^^^^^^^^^^^^^^^^^
uwsgi[62808]:   File "/usr/lib/python3/dist-packages/dasbus/client/proxy.py", line 164, in __getattr__
uwsgi[62808]:     return member.get()
uwsgi[62808]:            ^^^^^^^^^^^^
uwsgi[62808]:   File "/usr/lib/python3/dist-packages/dasbus/client/property.py", line 43, in get
uwsgi[62808]:     return self.__get__(None, None)  # pylint: disable=unnecessary-dunder-call
uwsgi[62808]:            ^^^^^^^^^^^^^^^^^^^^^^^^
uwsgi[62808]:   File "/usr/lib/python3/dist-packages/dasbus/client/property.py", line 54, in __get__
uwsgi[62808]:     return self._getter()
uwsgi[62808]:            ^^^^^^^^^^^^^^
uwsgi[62808]:   File "/usr/lib/python3/dist-packages/dasbus/client/handler.py", line 382, in _get_property_value
uwsgi[62808]:     variant = self._call_method(
uwsgi[62808]:               ^^^^^^^^^^^^^^^^^^
uwsgi[62808]:   File "/usr/lib/python3/dist-packages/dasbus/client/handler.py", line 450, in _call_method
uwsgi[62808]:     return self._get_method_reply(
uwsgi[62808]:            ^^^^^^^^^^^^^^^^^^^^^^^
uwsgi[62808]:   File "/usr/lib/python3/dist-packages/dasbus/client/handler.py", line 483, in _get_method_reply
uwsgi[62808]:     return self._handle_method_error(error)
uwsgi[62808]:            ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
uwsgi[62808]:   File "/usr/lib/python3/dist-packages/dasbus/client/handler.py", line 509, in _handle_method_error
uwsgi[62808]:     raise exception from None
uwsgi[62808]: dasbus.error.DBusError: Invalid DBus value 'None'.
uwsgi[62808]: [pid: 62808|app: 0|req: 2/13] 0.0.0.0 () {48 vars in 884 bytes} [Wed Jul 26 18:16:15 2023] GET /devs/keyring.asc => generated 265 bytes in 64 msecs (HTTP/1.0 500) 2 headers in 99 bytes (1 switches on core 0)