gtkada3 callback function & failure : subprogram must not be deeper than access type

[Alain De Vos <devosalain71@gmail.com>]

For callback functions there are 3 methods and one with data.
For the first method I try a program with one button
Connecting the button with the handler fails with the error :
>>>>subprogram must not be deeper than access type

The code :
-- TEST : Connecting via the On_* procedures first method
with Ada.Text_IO; use Ada.Text_IO;
with Glib;         use Glib;
with Glib.Object;  use Glib.Object;
with Gtk;          use Gtk;
with Gtk.Box;      use Gtk.Box;
with Gtk.Button;   use Gtk.Button;
with Gtk.Enums;    use Gtk.Enums;
with Gdk.Event;    use Gdk.Event;
with Gtk.Frame;    use Gtk.Frame;
with Gtk.Grid;     use Gtk.Grid;
with Gtk.Handlers; use Gtk.Handlers;
with Gtk.Label;    use Gtk.Label;
with Gtk.Main;     use Gtk.Main;
with Gtk.Widget;   use Gtk.Widget;
with Gtk.Window;   use Gtk.Window;
with Gtk.Main;   use Gtk.Main;

procedure hello_gtk is
   Main_Window : Gtk.Window.Gtk_Window;
   Button  : Gtk_Button;
   procedure On_Button_Click (Button : access Gtk_Button_Record'Class)
   is
   begin
      Put_line ("Hallo");
   end On_Button_Click;

   procedure Create_Window is
   begin
      Gtk.Window.Gtk_New
        (Window   => Main_Window,
         The_Type => Gtk.Enums.Window_Toplevel);
      Gtk.Window.Set_Title (Window => Main_Window, Title  => "Hello from ADA");
      --  Button.On_Clicked (On_Button_Click'Access); fails with subprogram must not be deeper than access type
      Add (Main_Window,Button);
      Gtk.Window.Show_All (Main_Window);
   end Create_Window;
begin
   Gtk.Main.Init;
   Create_Window;
   Gtk.Main.Main;
end hello_gtk;