[mb-users] Track duration is None

When I look up the track duration for a particular recording using the API 
thusly:

rel_filter = mbws.ReleaseFilter(discId='Uet7Ne0jNNwhz206YC0rPlDJELw-')
result = query.getReleases(rel_filter)
release = result[0].release
release.tracks[0].title
u'Adagio \u2013 Allegro molto'
print release.tracks[0].duration

I get None.

I figured that I should check the duration using the web interface, but I 
cannot find the recording.  It must be in the database -- right? -- because I 
get a result when I search using the API.  Is there a way to look up a 
recording using the disc ID?  How does it happen that the duration of the 
tracks on this recording are all None?  Is this record erroneous, or do I have 
to protect against this value?

Jeffrey Barish