Having the scripting functions is_complete() or matchedtracks() in naming script and saving a cluster causes an exception:

E: 17:22:37,525 /home/phw/devel/musicbrainz/picard/picard/util/thread.run:56: Traceback (most recent call last):
File "/home/phw/devel/musicbrainz/picard/picard/util/thread.py", line 52, in run
result = self.func()
File "/home/phw/devel/musicbrainz/picard/picard/file.py", line 269, in _save_and_rename
new_filename = self._rename(old_filename, metadata)
File "/home/phw/devel/musicbrainz/picard/picard/file.py", line 431, in _rename
self._make_filename(old_filename, metadata))
File "/home/phw/devel/musicbrainz/picard/picard/file.py", line 420, in _make_filename
new_filename = self._format_filename(new_dirname, new_filename, metadata, settings)
File "/home/phw/devel/musicbrainz/picard/picard/file.py", line 384, in _format_filename
new_filename = self._script_to_filename(naming_format, metadata, settings)
File "/home/phw/devel/musicbrainz/picard/picard/file.py", line 364, in _script_to_filename
return script_to_filename(naming_format, metadata, file=self, settings=settings)
File "/home/phw/devel/musicbrainz/picard/picard/util/scripttofilename.py", line 41, in script_to_filename
filename = ScriptParser().eval(naming_format, meta, file)
File "/home/phw/devel/musicbrainz/picard/picard/script.py", line 294, in eval
return ScriptParser._cache[key].eval(self)
File "/home/phw/devel/musicbrainz/picard/picard/script.py", line 133, in eval
return "".join([item.eval(state) for item in self])
File "/home/phw/devel/musicbrainz/picard/picard/script.py", line 133, in <listcomp>
return "".join([item.eval(state) for item in self])
File "/home/phw/devel/musicbrainz/picard/picard/script.py", line 127, in eval
return function(parser, *args)
File "/home/phw/devel/musicbrainz/picard/picard/script.py", line 720, in func_is_complete
if (file and file.parent and hasattr(file.parent, 'album')
AttributeError: 'Cluster' object has no attribute 'album'