opt(loop('A',None))

Rendering to test.png using cairo backend
Traceback (most recent call last):
  File "/usr/local/bin/syntrax", line 11, in <module>
    load_entry_point('syntrax==1.0', 'console_scripts', 'syntrax')()
  File "/usr/local/lib/python2.7/dist-packages/syntrax.py", line 2028, in main
    render_railroad(spec, args.title, url_map, args.output, backend, styles, args.scale, args.transparent)
  File "/usr/local/lib/python2.7/dist-packages/syntrax.py", line 1747, in render_railroad
    layout.draw_diagram(spec)
  File "/usr/local/lib/python2.7/dist-packages/syntrax.py", line 1678, in draw_diagram
    return self.draw_line(spec[1:])
  File "/usr/local/lib/python2.7/dist-packages/syntrax.py", line 1287, in draw_line
    t, texx, texy = self.draw_diagram(term) # Draw each element
  File "/usr/local/lib/python2.7/dist-packages/syntrax.py", line 1695, in draw_diagram
    return self.draw_or([None, args])
  File "/usr/local/lib/python2.7/dist-packages/syntrax.py", line 1604, in draw_or
    m[i] = mx = self.draw_diagram(term)
  File "/usr/local/lib/python2.7/dist-packages/syntrax.py", line 1673, in draw_diagram
    return self.draw_bubble(spec[0])
  File "/usr/local/lib/python2.7/dist-packages/syntrax.py", line 1206, in draw_bubble
    txt, node_style = self.format_text(txt)
  File "/usr/local/lib/python2.7/dist-packages/syntrax.py", line 1182, in format_text
    if re.match(ns.pattern, txt):
  File "/usr/lib/python2.7/re.py", line 141, in match
    return _compile(pattern, flags).match(string)
TypeError: expected string or buffer