After upgrading* to MusicBrainz v2.8.5, starting MusicBrainz gives:

> An unexpected error has caused Picard to crash. Please report this issue on the MusicBrainz bug tracker.

>

>Traceback (most recent call last):
>  File "config.py", line 345, in run_upgrade_hooks
>  File "config_upgrade.py", line 309, in upgrade_to_v2_4_0_beta_3
>AttributeError: 'list' object has no attribute 'split'

>During handling of the above exception, another exception occurred:

>Traceback (most recent call last):
>  File "tagger.py", line 17, in <module>
>  File "tagger.py", line 1083, in main
>  File "tagger.py", line 265, in {}init{}
>  File "config_upgrade.py", line 504, in upgrade_config
>  File "config.py", line 348, in run_upgrade_hooks
>picard.config.ConfigUpgradeError: Error during config upgrade from version 2.2.0.dev3 to 2.4.0.beta3 using upgrade_to_v2_4_0_beta_3():
>Traceback (most recent call last):
>  File "config.py", line 345, in run_upgrade_hooks
>  File "config_upgrade.py", line 309, in upgrade_to_v2_4_0_beta_3
>AttributeError: 'list' object has no attribute 'split'

*If I recall correctly the issue appeared after upgrading an earlier version than 2.8.5.