std::char::from_digit not working with print_char()

extern crate rustbox;

use rustbox::{Color, RustBox};
use std::char::from_digit;
use rustbox::Key;

fn main() {

    let rustbox = RustBox::init(Default::default()).ok().unwrap();
    for x in 0..rustbox.width() - 1 {
           rustbox.print_char(x, 0, rustbox::RB_NORMAL, Color::Black, Color::Cyan, '-');
    }

    for y in 0..rustbox.height() - 1 {
           rustbox.print_char(0, y + 1, rustbox::RB_NORMAL, Color::Black, Color::Blue, from_digit(y as u32, 10).unwrap());
    }

    loop {
        rustbox.present();
        match rustbox.poll_event(false) {
            Ok(rustbox::Event::KeyEvent(key)) => {
                match key {
                    Key::Char('q') => { break; }
                    _ => { }
                }
            },
            Err(e) => panic!("{}", e),
            _ => { }
        }
    }

}

The following program does not print anything to the screen whereas changing the from_digit() call to a hardcoded char value makes it run fine.

gchp / rustbox

std::char::from_digit not working with print_char() #76