Gtk::Style paint_box() cannot be used fully

[Philip Boulain <prb ecs soton ac uk>]

As for GTK+'s C API, Gtk::Style's paint_box() method is documented as 
accepting NULL (zero, specifically) for parameters such as "area". 
However, these parameters take references (e.g. "const Gdk::Rectangle& 
area"), and therefore zero cannot actually be passed to them.

API problem, or am I missing something? (Using the C version, gobj(), 
and some dubious casting between GTKmm and GTK+ enums appears to work fine.)

LionsPhil
1. 
http://www.gtkmm.org/docs/gtkmm-2.4/docs/reference/html/classGtk_1_1Style.html