unowned ObjectClass pclass = final_persona.get_class ();
=>
          GObjectClass* _tmp12_ = NULL;
          GObjectClass* pclass;
          GParamSpec* _tmp13_ = NULL;
          _tmp12_ = G_OBJECT_GET_CLASS ((GObject*) final_persona);
          pclass = _tmp12_;


var pclass = final_persona.get_class ();
=>
          GObjectClass* _tmp12_ = NULL;
          GObjectClass* _tmp13_;
          GObjectClass* pclass;
          GParamSpec* _tmp14_ = NULL;
          _tmp12_ = G_OBJECT_GET_CLASS ((GObject*) final_persona);
          _tmp13_ = _g_type_class_ref0 (_tmp12_);
          pclass = _tmp13_;

In this second case, _g_type_class_ref0 (_tmp12_) fails with:

GLib-GObject-WARNING **: cannot retrieve class for invalid (unclassed) type `(null)'

even though _tmp12_ is non-NULL.

The code for _g_type_class_ref0() looks fine:

static gpointer _g_type_class_ref0 (gpointer self) {
  return self ? g_type_class_ref (self) : NULL;
}