I'm running a local server, that I use to check my entire music collection against. Overnight, it generates a number of internal server errors.

A quick check of stderr found this reported:

[error] Caught exception in MusicBrainz::Server::Controller::WS::2::Release->release "Can't use an undefined value as an ARRAY reference at native delegation method MusicBrainz::Server::Entity::Artist::all_isni_codes (elements) of attribute isni_codes (defined at lib/MusicBrainz/Server/Entity/Role/ISNI.pm line 8) line 6."