CRITICAL **: signal 'bidule' is invalid

hot.c

@@ -13,6 +13,10 @@
 //  GTK_ORIENTATION_VERTICAL       GTK_ORIENTATION_HORIZONTAL
 
 
+static void on_experimental_expander_toggled(GtkExpander *expander, gpointer user_data){
+  gtk_expander_set_expanded (expander, gtk_expander_get_expanded (expander));
+}
+
 GtkBox *get_experimental_box_new(){
   GtkBox *experimental_box = GTK_BOX(gtk_box_new (GTK_ORIENTATION_VERTICAL, 0));
   gtk_box_append (experimental_box, GTK_WIDGET(gtk_separator_new (GTK_ORIENTATION_HORIZONTAL)));
@@ -21,7 +25,7 @@ GtkBox *get_experimental_box_new(){
   GtkExpander *hello = GTK_EXPANDER (gtk_expander_new ("hello !"));
   gtk_expander_set_expanded (GTK_EXPANDER (hello), TRUE);
   gtk_widget_set_margin_start (GTK_WIDGET (hello), 0);
-//  g_signal_connect(hello, "activate", G_CALLBACK(on_tree_expander_toggled), hello);
+  g_signal_connect (hello, "bidule", G_CALLBACK (on_experimental_expander_toggled), hello);
   gtk_box_append (experimental_box, GTK_WIDGET (hello));
 
   GtkExpander *it_s_me = GTK_EXPANDER (gtk_expander_new ("it's me !"));