Completing edit 159979, which cleared the literal string "none" from this field but reported that no English Wikipedia article could be verified. One can: https://en.wikipedia.org/wiki/Die_Verschworenen carries Category:Operas by Franz Schubert and opens "Die Verschworenen, also known as Der hausliche Krieg (D 787) is an 1823 one-act singspiel by Franz Schubert" - matching this record title and composer exactly. Found during an audit of edits 159875-159992.

Clearing a wikipediaUrl that held the literal string "none". It is not a URL and resolves to Wikipedia's "None" disambiguation page, so it is worse than an empty field: it looks like data. No English Wikipedia article for this opera could be verified by composer and title.