Unsupported operand type-error in Ubuntu 18.04.1 while playing music

Versions

• OS: Linux
• GTK+ Version: 3.22.30
• PyGObject Version: 3.26.1
• python-nbxmpp Version: 0.6.4
• Gajim Version: 1.0.1

Traceback

Traceback (most recent call last):
  File "/home/paul/.local/share/gajim/plugins/now_listen/now_listen.py", line 84, in music_track_changed
    log.debug(self.artist + " - " + self.title)
TypeError: unsupported operand type(s) for +: 'NoneType' and 'str'

Steps to reproduce the problem

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