Crash with fullrelease() during OSI build

[rezib]

In latest release 2.0.0, an attempt to build OSI images gives the following error while retrieving the fullrelease() on server side:

fatbuildrd[49337]: Exception in thread worker-default:
fatbuildrd[49337]: Traceback (most recent call last):
fatbuildrd[49337]:   File "/usr/lib/python3.10/threading.py", line 1016, in _bootstrap_inner
fatbuildrd[49337]:     self.run()
fatbuildrd[49337]:   File "/usr/lib/python3.10/threading.py", line 953, in run
fatbuildrd[49337]:     self._target(*self._args, **self._kwargs)
fatbuildrd[49337]:   File "/usr/lib/python3/dist-packages/fatbuildr/cli/fatbuildrd.py", line 133, in _worker
fatbuildrd[49337]:     instance.tasks_mgr.run(task)
fatbuildrd[49337]:   File "/usr/lib/python3/dist-packages/fatbuildr/tasks/manager.py", line 177, in run
fatbuildrd[49337]:     task.run()
fatbuildrd[49337]:   File "/usr/lib/python3/dist-packages/fatbuildr/builds/__init__.py", line 225, in run
fatbuildrd[49337]:     self.prepare()
fatbuildrd[49337]:   File "/usr/lib/python3/dist-packages/fatbuildr/builds/__init__.py", line 258, in prepare
fatbuildrd[49337]:     self.defs.fullversion(self.derivative)
fatbuildrd[49337]:   File "/usr/lib/python3/dist-packages/fatbuildr/artifact.py", line 234, in fullversion
fatbuildrd[49337]:     self.source(self.artifact).version(derivative) + '-' + self.release
fatbuildrd[49337]: TypeError: can only concatenate str (not "int") to str