Key Signature none in Match Export #261
Description
The following issue occurs for empty Key signatures in match export.
...
File "/miniconda3/envs/asap/lib/python3.10/site-packages/partitura/io/matchfile_utils.py", line 689, in __str__
ks = fifths_mode_to_key_name(self.fifths, self.mode)
File "/miniconda3/envs/asap/lib/python3.10/site-packages/partitura/utils/music.py", line 736, in fifths_mode_to_key_name
raise Exception("Unknown mode {}".format(mode))
Exception: Unknown mode none