`gtk_menu_button_set_child` prints warning when argument is `NULL`

MWE

GtkWidget* button = gtk_menu_button_new();
gtk_menu_button_set_child(GTK_MENU_BUTTON(button), NULL);

prints

(test_main:257197): Gtk-CRITICAL **: 21:24:23.846: gtk_box_append: assertion 'GTK_IS_WIDGET (child)' failed

Even though the docs say that the child argument can be NULL. Setting the child to NULL works as expected, it's only the warning that is being erroneously printed.

Tested with GTK4.10, on fedora linux.