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>

tests/unit/injectionManager.js

@@ -21,7 +21,7 @@ class Object1 {
 class GObject1 extends GObject.Object {
     static [GObject.properties] = {
         'plonked': GObject.ParamSpec.boolean(
-            'plonked', '', '',
+            'plonked', null, null,
             GObject.ParamFlags.READWRITE,
             false),
     };