Crash on retrieving derivative version

[rezib]

The fatbuildrd daemon crashes when retrieving the version of an artifact for a derivative:

fatbuildrd[601701]: worker-default: [DEBUG] fatbuildr.artifact Loading artifact definitions from /var/lib/fatbuildr/workspaces/default/bb07992a-26f0-43a0-abfe-97aeac17bd84/artifact.yml
fatbuildrd[601701]: Exception in thread worker-default:
fatbuildrd[601701]: Traceback (most recent call last):
fatbuildrd[601701]:   File "/usr/lib/python3.10/threading.py", line 1016, in _bootstrap_inner
fatbuildrd[601701]:     self.run()
fatbuildrd[601701]:   File "/usr/lib/python3.10/threading.py", line 953, in run
fatbuildrd[601701]:     self._target(*self._args, **self._kwargs)
fatbuildrd[601701]:   File "/usr/lib/python3/dist-packages/fatbuildr/cli/fatbuildrd.py", line 133, in _worker
fatbuildrd[601701]:     instance.tasks_mgr.run(task)
fatbuildrd[601701]:   File "/usr/lib/python3/dist-packages/fatbuildr/tasks/manager.py", line 177, in run
fatbuildrd[601701]:     task.run()
fatbuildrd[601701]:   File "/usr/lib/python3/dist-packages/fatbuildr/builds/__init__.py", line 225, in run
fatbuildrd[601701]:     self.prepare()
fatbuildrd[601701]:   File "/usr/lib/python3/dist-packages/fatbuildr/builds/__init__.py", line 258, in prepare
fatbuildrd[601701]:     self.defs.fullversion(self.derivative)
fatbuildrd[601701]:   File "/usr/lib/python3/dist-packages/fatbuildr/artifact.py", line 233, in fullversion
fatbuildrd[601701]:     self.source(self.artifact).version(derivative) + '-' + self.release
fatbuildrd[601701]:   File "/usr/lib/python3/dist-packages/fatbuildr/artifact.py", line 76, in version
fatbuildrd[601701]:     return str(self.defs['derivatives'][derivative]['version'])
fatbuildrd[601701]: TypeError: string indices must be integers