gbr: Sent job ' - - '

[mats_a]

I notice that occasionally, some files will be sent as ' - - ' when doing gbr:

Use of uninitialized value in concatenation (.) or string at /usr/bin/gbr line 55.
Use of uninitialized value in concatenation (.) or string at /usr/bin/gbr line 55.
Use of uninitialized value in concatenation (.) or string at /usr/bin/gbr line 55.
Sent job ' -  - ' (id 22120)

I only have 2 datapoints.
It seems to be the case that the files which triggered this were an audio/mpeg file labelled as .mp3 which was misidentified by gutenbach as .ogg, and a video/mpeg file labelled as .mp3 which was misidentified by gutenbach as m4a. Interestingly, gutenbach seems to recognize and output the correct metadata, though it lists the file as ' - - '; however on my end, running exiftool does not return any album/artist/etc. metadata.