stack trace:
Traceback (most recent call last):
File ./scan, line 27, in <module>
for a in tracks_to_tag_cache_format(tracks):
File /home/martins/source/mopidy/mopidy/frontends/mpd/translator.py, line 138, in tracks_to_tag_cache_format
_add_to_tag_cache(result, *tracks_to_directory_tree(tracks))
File /home/martins/source/mopidy/mopidy/frontends/mpd/translator.py, line 151, in _add_to_tag_cache
_add_to_tag_cache(result, *entry)
File /home/martins/source/mopidy/mopidy/frontends/mpd/translator.py, line 156, in _add_to_tag_cache
track_result = dict(track_to_mpd_format(track))
File /home/martins/source/mopidy/mopidy/frontends/mpd/translator.py, line 28, in track_to_mpd_format
('Artist', artists_to_mpd_format(track.artists)),
File /home/martins/source/mopidy/mopidy/frontends/mpd/translator.py, line 88, in artists_to_mpd_format
return u', '.join([a.name for a in artists if a])
TypeError: sequence item 0: expected string or Unicode, NoneType found