[gtkada] Treeview Set_Model

[Manuel Op de Coul]

I'm using this procedure from Gtk.Tree_View.

   procedure Set_Model
     (Tree_View : access Gtk_Tree_View_Record;
      Model     : Gtk.Tree_Model.Gtk_Tree_Model);
   --  Sets the model for a Gtk_Tree_View.  If the Tree_View already has a
   --  model set, it will remove it before setting the new model.
   --  If Model is Null, then it will unset the old model.

The last sentence is what I intend to do, and use null for the
Model parameter.
However then a Constraint_Error is raised in gtk-tree-view.adb:139.
Did I miss something?

Manuel