ServiceUnknown during boot, causes daemon to crash

[wdoekes]

Crash during boot:

> Please insert your hardware token for extra authentication. When it blinks, touch the button.
Traceback (most recent call last):
  File "/etc/openvpn/openvpn-u2f-setup/openvpn-u2f-ask-password", line 671, in <module>
    reread_existing()
  File "/etc/openvpn/openvpn-u2f-setup/openvpn-u2f-ask-password", line 656, in reread_existing
    handler.handle_askfile(os.path.join(ASK_PASSWORD_DIRECTORY, filename))
  File "/etc/openvpn/openvpn-u2f-setup/openvpn-u2f-ask-password", line 550, in handle_askfile
    self._handle_askinifile(pathname, data)
  File "/etc/openvpn/openvpn-u2f-setup/openvpn-u2f-ask-password", line 577, in _handle_askinifile
    ask.handle()
  File "/etc/openvpn/openvpn-u2f-setup/openvpn-u2f-ask-password", line 382, in handle
    self._handle_username_request()
  File "/etc/openvpn/openvpn-u2f-setup/openvpn-u2f-ask-password", line 405, in _handle_username_request
    keyhandle, timestamp, response = self._make_challenge_response(
  File "/etc/openvpn/openvpn-u2f-setup/openvpn-u2f-ask-password", line 501, in _make_challenge_response
    note.show()
  File "/etc/openvpn/openvpn-u2f-setup/openvpn-u2f-ask-password", line 152, in show
    self._notification.show()
gi.repository.GLib.Error: g-dbus-error-quark: GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown: The name :1.41 was not provided by any .service files (2)

openvpn-u2f-ask-password.service: Main process exited, code=exited, status=1/FAILURE
openvpn-u2f-ask-password.service: Failed with result 'exit-code'.

Possible workaround:

--- a/openvpn-u2f-ask-password
+++ b/openvpn-u2f-ask-password
@@ -31,7 +31,7 @@ try:
     # "ValueError: Namespace Notify not available for version 0.8"
     gi.require_version('Notify', '0.7')  # hide version warning
 
-    from gi.repository import Notify as GObjectNotify
+    from gi.repository import Notify as GObjectNotify, GLib
 
     # We expect python3-dbus through these dependent apt packages:
     #   ubuntu-server -> software-properties-common -> python3-dbus
@@ -149,7 +149,15 @@ class Notification:
 
     def show(self):
         if self._notification:
-            self._notification.show()
+            try:
+                self._notification.show()
+            except GLib.Error as e:
+                # (Observed during boot.)
+                # gi.repository.GLib.Error: g-dbus-error-quark:
+                #   GDBus.Error:org.freedesktop.DBus.Error.ServiceUnknown:
+                #   The name :1.41 was not provided by any .service files (2)
+                print('ERROR showing notification: {}'.format(e))
+
         print('> [{}]\n> {}'.format(self._title, self._body))