Use NULL for nick/blurb in GObject params

As they are only used by gstreamer for gst-inspect & other tools.
Projects like Mutter/gtk have completely dropped them as well, so follow
their path

Part-of: <https://gitlab.gnome.org/GNOME/gnome-shell/-/merge_requests/3505>

js/ui/status/backgroundApps.js

@@ -25,10 +25,10 @@ Gio._promisify(Gio.DBusConnection.prototype, 'call');
 
 const BackgroundAppMenuItem = GObject.registerClass({
     Properties: {
-        'app': GObject.ParamSpec.object('app', '', '',
+        'app': GObject.ParamSpec.object('app', null, null,
             GObject.ParamFlags.READWRITE,
             Shell.App),
-        'message': GObject.ParamSpec.string('message', '', '',
+        'message': GObject.ParamSpec.string('message', null, null,
             GObject.ParamFlags.READWRITE,
             null),
     },