typerror when hitting the 'convert' button

[Vinicius Massuchetto]

I get this after adding directories, configuring a MP3->MP3 conversion, and clicking on the "convert" button:

    Traceback (most recent call last):
      File "/usr/lib/soundconverter/python/soundconverter/ui.py", line 1323, in on_convert_button_clicked
        self.do_convert()
      File "/usr/lib/soundconverter/python/soundconverter/ui.py", line 1309, in do_convert
        self.converter.start()
      File "/usr/lib/soundconverter/python/soundconverter/gstreamer.py", line 804, in start
        self.waiting_tasks.sort(key=Converter.get_duration,reverse=True)
    TypeError: '<' not supported between instances of 'NoneType' and 'float'

Using SoundConverter 2.9.0-beta2 on Arch Linux.