TitleReaderPlugin: return None triggers exception

[dentarg]

[23:01:24] RECV: :[email protected] PRIVMSG #foo :http://example.org/image.png
argh <TitleReaderPlugin []> (<type 'exceptions.TypeError'>, TypeError("object of type 'NoneType' has no
 len()",), <traceback object at 0x7f25d299fcb0>) [('/home/rufwebot/pynik/ircbot.py', 64, 'execute_plugins',
 'plugin.__class__.__dict__[trigger](plugin, self, *arguments)'),
 ('/home/rufwebot/pynik/plugins/title_reader.py', 75, 'on_privmsg', 'bot.tell(target, self.clean(url, title))'),
 ('/home/rufwebot/pynik/ircbot.py', 112, 'tell', 'return self.client.tell(target, message)'),
 ('/home/rufwebot/pynik/ircclient/ircclient.py', 91, 'tell', 'if len(string) >= 399:')]

[dentarg]

The exception happen whenever we return None from get_title