Last modified: 2013-06-24 18:39:54 UTC
Which fails validation: ValidationError: None is not of type u'string'
Related URL: https://gerrit.wikimedia.org/r/69966 (Gerrit Change I1626af38640c921e616be05f93d42ba795eaaf01)
I researched this more carefully and determined that this error last occurred in April, with revision 5303086 of the schema (<https://meta.wikimedia.org/wiki/Schema:PageContentSaveComplete?oldid=5303086>). It could be edifying to go back and figure out the exact source of the bug, but I don't expect to have the time for it.